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Install
Bow and stern thruster batteries: cranking amps and placement
A thruster only pushes as hard as its battery lets it. This page shows you what the thruster makers ask for. They want a battery sized in Cold cranking amps: how much current a battery can deliver in a short, hard burst, which is the rating starter batteries carry. A thruster draws like a starter, so the makers size its battery this way rather than by capacity., sitting close to the thruster. It must be a type that holds its voltage while the motor draws several hundred amps. Get any of the three wrong and the thruster never delivers the number on its box.
Sleipner puts the whole idea in one sentence in its manual. It is the actual voltage at the motor while the thruster is running that decides the thrust you get. Everything below works that sentence through in the makers’ own figures, with the arithmetic shown.
A stern thruster's battery comes from its maker's figure too. The battery calculator holds the maker's battery figure or rule for 27 of the 28 units made only for the stern that it lists.
The cable half of the job, gauge and fuse, is on the wiring page. Whether you should be doing any of this yourself is on the DIY page.
The short answer
The makers rate a thruster battery the way starter batteries are rated. Sleipner’s minimums work out to about 0.82 to 1.18 One of two test standards for a battery’s cold cranking amps, the German one. It gives a lower number than the American test for the same battery. Check which standard a label uses before comparing figures. cranking amps for every amp the motor draws.
Sleipner, VETUS and Sideshift all say so. On the SE100/185T, a battery 5 feet away loses about 4% of its voltage in the cable. At 20 feet the loss is about 15%.
Sleipner’s own thrust figures fall by 12% to 25% when the battery sags under load. On a proportional thruster a weak battery costs run time instead.
Sideshift asks for a starting battery and advises against deep cycle. Lithium depends on the thruster, so ask the maker about your model before you buy one.
Batteries, cable and charger run $483–$4,767 across the tunnel units on this site, priced unit by unit.
Choose the battery in four steps
- Find the cranking figure for your thruster. Look up your model’s minimum in the maker’s table. In a US marine store, read the One of two test standards for a battery’s cold cranking amps, the American one. It is the figure on most battery labels sold in the US. It gives a higher number than the German test for the same battery. figure on the label. The tables are in the section “Why the makers size in cranking amps”.
- Put the battery near the thruster. The makers want the heavy cable to the motor kept short. A small charging lead runs back to the rest of the boat instead. The section “Where the bank lives” shows what a long cable costs.
- Pick the type your maker names. The answer changes with the thruster, and lithium most of all. The section “Starting, deep cycle, AGM, lithium” quotes each maker.
- Plan the charging, then check the voltage. A battery up forward needs its own way to charge. Once it is in, measure the voltage at the thruster. The section “Charging a bank that lives in the bow” has what each maker says.
Want the numbers for your own boat? The battery calculator gives the battery each maker asks for and checks yours against it. The wiring calculator sizes the cable for your run. If you have not picked a thruster yet, the thruster finder, our free tool that matches a thruster to your boat, is the place to start.
The battery decides the thrust, in the makers’ own numbers
Sleipner prints two thrust figures for most of its models. One is at full battery voltage. The other is at the voltage a lead-acid battery The drop in a battery’s voltage while a heavy load is drawing from it. The battery recovers when the load stops, but the motor only ever sees the sagged figure. to under a heavy draw, which is 10.5 volts on a 12 volt system. Both figures are the maker’s. The gap between them is the cost of a weak supply.
Show Sleipner’s thrust at full and sagged voltage (49 rows)
| Model | At full voltage | Sagged | Thrust lost |
|---|---|---|---|
| Sleipner Side-Power SE25/110S, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 66 lb at 12V/24V | 55 lb at 10.5V/21V | 17% |
| Sleipner Side-Power SE30/125S DC, thrust at two voltages
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 88 lb at 12V | 66 lb at 10.5V | 25% |
| Sleipner Side-Power SE30/125S-IP, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 88 lb at 12V | 66 lb at 10.5V | 25% |
| Sleipner Side-Power SX35 Compact Stern, thrust at two voltages
Defender listing, read 12 October 2026. Full page: fit, cost and wiring See it on Defender | 93 lb at 12V | 77 lb at 10.5V | 17% |
| Sleipner Side-Power SE40/125S, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 105 lb at 12V | 88 lb at 10.5V | 16% |
| Sleipner Side-Power SEP40/125S-1IP, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 105 lb at 12V | 88 lb at 10.5V | 16% |
| Sleipner Side-Power SEP40/125S, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 106 lb at 12V | 88 lb at 10.5V | 17% |
| Sleipner Side-Power SE50/140S, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 136 lb at 12V | 110 lb at 10.5V | 19% |
| Sleipner Side-Power SX50 Compact Stern Thruster, thrust at two voltages
Defender listing, read 12 October 2026. Full page: fit, cost and wiring See it on Defender | 137 lb at 12V/24V | 110 lb at 10.5V/21V | 20% |
| Sleipner Side-Power SEP50/140S, thrust at two voltages
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 137 lb at 12V | 110 lb at 10.5V | 20% |
| Sleipner Side-Power SE60/185S, thrust at two voltages
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 161 lb at 12V | 132 lb at 10.5V | 18% |
| Sleipner Side-Power SEP60/185S, thrust at two voltages
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 161 lb at 12V | 132 lb at 10.5V | 18% |
| Sleipner Side-Power SX80, thrust at two voltages
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SXP80 PRO, thrust at two voltages
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SR80, thrust at two voltages
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SRL80, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SRLP80 PRO, thrust at two voltages
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SRP80 PRO, thrust at two voltages
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SRV80, thrust at two voltages
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 212 lb at 24V | 176 lb at 21V | 17% |
| Sleipner Side-Power SRVP80 PRO, thrust at two voltages
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SE80/185T, thrust at two voltages
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SEP80/185T, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 212 lb at 12V | 176 lb at 10.5V | 17% |
| Sleipner Side-Power SX100, thrust at two voltages
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SXP100 PRO, thrust at two voltages
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SR100, thrust at two voltages
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SRL100, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SRLP100 PRO, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SRP100 PRO, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SRV100, thrust at two voltages
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SRVP100 PRO, thrust at two voltages
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SE100/185T, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 256 lb at 12V | 220 lb at 10.5V | 14% |
| Sleipner Side-Power SE120/215T-24V, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 306 lb at 24V | 264 lb at 21V | 14% |
| Sleipner Side-Power SEP120/215T-24V, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 306 lb at 24V | 265 lb at 21V | 13% |
| Sleipner Side-Power SE130/250T, thrust at two voltages
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 352 lb at 12V | 286 lb at 10.5V | 19% |
| Sleipner Side-Power SEP130/250T, thrust at two voltages
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 352 lb at 12V | 284 lb at 10.5V | 19% |
| Sleipner Side-Power SRL130, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 353 lb at 12V | 287 lb at 10.5V | 19% |
| Sleipner Side-Power SRLP130 PRO, thrust at two voltages
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 353 lb at 12V | 287 lb at 10.5V | 19% |
| Sleipner Side-Power SRV130, thrust at two voltages
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 353 lb at 12V | 287 lb at 10.5V | 19% |
| Sleipner Side-Power SE150/215T-24V, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 400 lb at 24V | 330 lb at 21V | 18% |
| Sleipner Side-Power SRL170, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 463 lb at 24V | 375 lb at 21V | 19% |
| Sleipner Side-Power SRV170, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 463 lb at 24V | 375 lb at 21V | 19% |
| Sleipner Side-Power SE170/250TC, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 463 lb at 24V | 375 lb at 21V | 19% |
| Sleipner Side-Power SEP170/250TC-IP, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 463 lb at 24V | 375 lb at 21V | 19% |
| Sleipner Side-Power SE210/250TC, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 550 lb at 24V | 462 lb at 21V | 16% |
| Sleipner Side-Power SEP210/250TC, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 550 lb at 24V | 462 lb at 21V | 16% |
| Sleipner Side-Power SRV210, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 551 lb at 24V | 463 lb at 21V | 16% |
| Sleipner Side-Power SE250/300TC, thrust at two voltages
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 661 lb at 24V | 551 lb at 21V | 17% |
| Sleipner Side-Power SRV300, thrust at two voltages
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 750 lb at 48V | 661 lb at 42V | 12% |
| Sleipner Side-Power SE300/300TC, thrust at two voltages
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 750 lb at 48V | 661 lb at 42V | 12% |
The loss runs from 12% to 25% across the 49 models that print both figures. It is worst on the SE30/125S.
Take the SE60/185S as an example. It is 161 lb on the box, and 132 lb once the battery is down to 10.5V. That lower figure is what the maker says the unit does on a supply that sags. A tired battery, a long thin cable or a corroded terminal can each get you there.
If your electrical side is going to be marginal, read the size calculator against the lower figure.
On/off and proportional thrusters
Most DC thrusters are on/off. Press the joystick and the motor runs flat out at whatever voltage the battery gives it. That is why the table above reads the way it does.
A A thruster with a controller between the battery and the motor, so the joystick sets how hard it pushes rather than just on or off. The motor and the mounting are the same. Only the control differs. puts a controller between the battery and the motor, so the joystick sets how hard it pushes. That controller changes what a weak battery costs. Proportional is a control type. VETUS’s BOW PRO range and Sleipner’s SEP and eVision ranges are proportional versions of the same A tube bored straight through the hull below the waterline, with a propeller in the middle of it. It is the conventional thruster. Fitting one is mostly a labor job rather than a hardware one. and A thruster that lives inside the hull and drops down through a hatch when you press the button, then pulls back up. It leaves no permanent hole in the water flow. motors.
VETUS explains it in the BOW PRO manual: “The thrust delivered is, within certain limits, not dependent on the battery voltage.” The controller holds the thrust as the voltage falls by drawing more current. At 10.5 volts on a 12 volt system (21 on 24) it starts reducing power. At about 10 volts (20 on 24) it stops.
The same manual says what the battery buys you instead: “The runtime is mainly limited by the capacity of the installed batteries.” (VETUS BOW PRO manual).
On an on/off unit a weak battery costs thrust. On a proportional one it costs run time. The run-time page has every maker’s limit.
A thruster that has gone weak on a boat where it used to be fine has a fault to find first. The troubleshooting page covers that, under what to check when it turns but pushes nothing.
Why the makers size in cranking amps
A The batteries that run the boat’s lights, fridge and electronics, as distinct from the engine’s starting battery. They are built for a slow, steady draw. is bought in How much a battery can supply slowly, over hours: ten amps for ten hours is a hundred amp-hours. It is the right measure for lights and a fridge. It is the wrong one for a thruster, which wants a lot of current for a few seconds., because a house load is small and long. A thruster load is the opposite: several hundred amps for seconds at a time.
That is a starter motor’s job. So every maker that prints a figure prints it the way starter batteries are rated, in Cold cranking amps: how much current a battery can deliver in a short, hard burst, which is the rating starter batteries carry. A thruster draws like a starter, so the makers size its battery this way rather than by capacity..
Show Sleipner’s draw and minimum battery by model (127 rows)
| Model | Volts | Draw | Min Cold cranking amps: how much current a battery can deliver in a short, hard burst, which is the rating starter batteries carry. A thruster draws like a starter, so the makers size its battery this way rather than by capacity., One of two test standards for a battery’s cold cranking amps, the German one. It gives a lower number than the American test for the same battery. Check which standard a label uses before comparing figures. | Min CCA, One of two test standards for a battery’s cold cranking amps, the American one. It is the figure on most battery labels sold in the US. It gives a higher number than the German test for the same battery. | The minimum battery the maker asks for, divided by the current the motor draws. A ratio near one means the maker wants a battery that can crank roughly what the thruster pulls. |
|---|---|---|---|---|---|
| Sleipner Side-Power SE30/125S DC, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 245 A | 200 A | 380 A | 0.82 |
| Sleipner Side-Power SE40/125S, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 315 A | 300 A | 570 A | 0.95 |
| Sleipner Side-Power SE60/185S, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SE80/185T, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SE80/185T, 24 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SE100/185T, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SE100/185T, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SE120/215T-24V, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 420 A | 450 A | 855 A | 1.07 |
| Sleipner Side-Power SE130/250T, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 800 A | 750 A | 1425 A | 0.94 |
| Sleipner Side-Power SE130/250T, 24 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 24 | 350 A | 400 A | 760 A | 1.14 |
| Sleipner Side-Power SE150/215T-24V, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 610 A | 560 A | 1064 A | 0.92 |
| Sleipner Side-Power SE170/250TC, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 550 A | 560 A | 1064 A | 1.02 |
| Sleipner Side-Power SE210/250TC, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 500 A | 560 A | 1064 A | 1.12 |
| Sleipner Side-Power SEP40/125S, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 315 A | 300 A | 570 A | 0.95 |
| Sleipner Side-Power SEP60/185S, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SEP60/185S, 24 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 24 | 170 A | 175 A | 332 A | 1.03 |
| Sleipner Side-Power SEP80/185T-IP, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SEP80/185T, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SEP80/185T, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SEP100/185T, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SEP100/185T, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SEP120/215T-24V, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 420 A | 450 A | 855 A | 1.07 |
| Sleipner Side-Power SEP130/250T, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 800 A | 750 A | 1425 A | 0.94 |
| Sleipner Side-Power SEP100/185T-IP, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SEP100/185T-IP, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SEP170/250TC-IP, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 550 A | 560 A | 1064 A | 1.02 |
| Sleipner Side-Power SEP210/250TC, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 500 A | 560 A | 1064 A | 1.12 |
| Sleipner Side-Power SEP40/125S-1IP, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 315 A | 300 A | 570 A | 0.95 |
| Sleipner Side-Power SEP60/185S-IP, 12 V, minimum battery
Defender listing, read 12 October 2026. Full page: fit, cost and wiring See it on Defender | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SEP60/185S-IP, 24 V, minimum battery
Defender listing, read 12 October 2026. Full page: fit, cost and wiring See it on Defender | 24 | 170 A | 175 A | 332 A | 1.03 |
| Sleipner Side-Power SE25/110S, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 200 A | 200 A | 380 A | 1.00 |
| Sleipner Side-Power SE30/125S-IP, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 245 A | 200 A | 380 A | 0.82 |
| Sleipner Side-Power SE40/125S-IP, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 315 A | 300 A | 570 A | 0.95 |
| Sleipner Side-Power SE50/140S, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SE60/185S, 24 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 24 | 170 A | 175 A | 332 A | 1.03 |
| Sleipner Side-Power SE60/185S-IP, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SE80/185T-IP, 12 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SE80/185T-IP, 24 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SE100/185T-IP, 12 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SE100/185T-IP, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SE250/300TC, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 670 A | 700 A | 1330 A | 1.04 |
| Sleipner Side-Power E100/185T, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 290 A | 290 A | 551 A | 1.00 |
| Sleipner Side-Power E100/185T, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 132 A | 132 A | 251 A | 1.00 |
| Sleipner Side-Power E120/215T, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 330 A | 330 A | 627 A | 1.00 |
| Sleipner Side-Power E120/215T, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 170 A | 170 A | 323 A | 1.00 |
| Sleipner Side-Power E130/250T, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 270 A | 270 A | 513 A | 1.00 |
| Sleipner Side-Power E130/250T, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 160 A | 160 A | 304 A | 1.00 |
| Sleipner Side-Power E150/215T, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 430 A | 430 A | 817 A | 1.00 |
| Sleipner Side-Power E150/215T, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 210 A | 210 A | 399 A | 1.00 |
| Sleipner Side-Power E170/250TC, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 395 A | 395 A | 751 A | 1.00 |
| Sleipner Side-Power E170/250TC, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 200 A | 200 A | 380 A | 1.00 |
| Sleipner Side-Power E210/250TC, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 580 A | 580 A | 1102 A | 1.00 |
| Sleipner Side-Power E210/250TC, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 290 A | 290 A | 551 A | 1.00 |
| Sleipner Side-Power E250/300TC, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 580 A | 580 A | 1102 A | 1.00 |
| Sleipner Side-Power E250/300TC, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 295 A | 295 A | 561 A | 1.00 |
| Sleipner Side-Power E300/300TC, 48 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 48 | 360 A | 360 A | 684 A | 1.00 |
| Sleipner Side-Power E420 eVision, 48 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 48 | 545 A | 545 A | 1035 A | 1.00 |
| Sleipner Side-Power SR80, 12 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SR100, 12 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SRV80, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SRV100, 12 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SRLP80 PRO, 24 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SRLP130 PRO, 12 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 12 | 800 A | 750 A | 760 A | 0.94 |
| Sleipner Side-Power ERL100 eVision, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 300 A | 300 A | 570 A | 1.00 |
| Sleipner Side-Power ERL130 eVision, 48 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 48 | 180 A | 180 A | 342 A | 1.00 |
| Sleipner Side-Power ERL170 eVision, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 225 A | 225 A | 428 A | 1.00 |
| Sleipner Side-Power ERV300 eVision, 48 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 48 | 395 A | 395 A | 751 A | 1.00 |
| Sleipner Side-Power SX35 Compact Stern, 12 V, minimum battery
Defender listing, read 12 October 2026. Full page: fit, cost and wiring See it on Defender | 12 | 245 A | 200 A | 380 A | 0.82 |
| Sleipner Side-Power SX50 Compact Stern Thruster, 12 V, minimum battery
Defender listing, read 12 October 2026. Full page: fit, cost and wiring See it on Defender | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SX80, 12 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SX80, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SX100, 12 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SX100, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SXP80 PRO, 12 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SXP80 PRO, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SXP100 PRO, 12 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SXP100 PRO, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SXE100 eVision, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 290 A | 290 A | 551 A | 1.00 |
| Sleipner Side-Power SR80, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SR100, 24 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SRL80, 12 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SRL80, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SRL100, 12 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SRL100, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SRV80, 12 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SRV100, 24 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SRLP80 PRO, 12 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SRP80 PRO, 12 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SRP80 PRO, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SRLP100 PRO, 12 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SRLP100 PRO, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SRVP80 PRO, 12 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 530 A | 550 A | 1045 A | 1.04 |
| Sleipner Side-Power SRVP80 PRO, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 280 A | 300 A | 570 A | 1.07 |
| Sleipner Side-Power SRVP100 PRO, 12 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 740 A | 750 A | 1425 A | 1.01 |
| Sleipner Side-Power SRVP100 PRO, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 340 A | 400 A | 760 A | 1.18 |
| Sleipner Side-Power SRLP130 PRO, 24 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 350 A | 400 A | 760 A | 1.14 |
| Sleipner Side-Power SRL130, 12 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 12 | 800 A | 750 A | 760 A | 0.94 |
| Sleipner Side-Power SRL130, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 350 A | 400 A | 760 A | 1.14 |
| Sleipner Side-Power SRL170, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 550 A | 560 A | 1064 A | 1.02 |
| Sleipner Side-Power SRV130, 12 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 800 A | 750 A | 760 A | 0.94 |
| Sleipner Side-Power SRV130, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 350 A | 400 A | 760 A | 1.14 |
| Sleipner Side-Power SRV170, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 550 A | 560 A | 1064 A | 1.02 |
| Sleipner Side-Power SRV210, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 500 A | 560 A | 1064 A | 1.12 |
| Sleipner Side-Power SRV300, 48 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 48 | 450 A | 400 A | 760 A | 0.89 |
| Sleipner Side-Power ERL100 eVision, 48 V, minimum battery
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 150 A | 150 A | 285 A | 1.00 |
| Sleipner Side-Power ERV100 eVision, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 300 A | 300 A | 570 A | 1.00 |
| Sleipner Side-Power ERV100 eVision, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 150 A | 150 A | 285 A | 1.00 |
| Sleipner Side-Power ERL130 eVision, 24 V, minimum battery
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 300 A | 300 A | 570 A | 1.00 |
| Sleipner Side-Power ERL170 eVision, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 420 A | 420 A | 798 A | 1.00 |
| Sleipner Side-Power ERV130 eVision, 24 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 24 | 300 A | 300 A | 570 A | 1.00 |
| Sleipner Side-Power ERV130 eVision, 48 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 48 | 180 A | 180 A | 342 A | 1.00 |
| Sleipner Side-Power ERV170 eVision, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 420 A | 420 A | 798 A | 1.00 |
| Sleipner Side-Power ERV170 eVision, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 225 A | 225 A | 428 A | 1.00 |
| Sleipner Side-Power ERV210 eVision, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 600 A | 600 A | 1140 A | 1.00 |
| Sleipner Side-Power ERV210 eVision, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 320 A | 320 A | 608 A | 1.00 |
| Sleipner Side-Power ERV250 eVision, 48 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 48 | 350 A | 350 A | 665 A | 1.00 |
| Sleipner Side-Power E240/250TC, 48 V, minimum battery
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 48 | 330 A | 330 A | 627 A | 1.00 |
| Sleipner Side-Power E340 eVision, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 545 A | 580 A | 1102 A | 1.06 |
| Sleipner Side-Power E350 HD eVision, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 545 A | 545 A | 1035 A | 1.00 |
| Sleipner Side-Power E350 HDB eVision, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 545 A | 545 A | 1035 A | 1.00 |
| Sleipner Side-Power SE300/300TC, 48 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 48 | 450 A | 400 A | 760 A | 0.89 |
| Sleipner Side-Power SE60/185S-IP, 24 V, minimum battery
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 24 | 170 A | 175 A | 332 A | 1.03 |
| Sleipner Side-Power SEP50/140S, 12 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SEP50/140S, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 170 A | 175 A | 332 A | 1.03 |
| Sleipner Side-Power SEP50/140S-IP, 12 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 12 | 370 A | 350 A | 665 A | 0.95 |
| Sleipner Side-Power SEP50/140S-IP, 24 V, minimum battery
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 24 | 170 A | 175 A | 332 A | 1.03 |
| Sleipner Side-Power SEP80/185T-IP, 24 V, minimum battery
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 280 A | 300 A | 570 A | 1.07 |
Read down the last column and a rule falls out. Sleipner never states it, but plainly uses it: about 0.82 to 1.18 DIN cranking amps per amp the motor draws. In plain terms, that is a battery that can crank roughly what the thruster pulls.
One row needs a note, the SE130 at 12 volts. The 2015 copy of its manual printed 760 A against DIN 400, the same minimum as the 24 V unit. That is 0.53 cranking amps per amp.
The maker’s current guide prints 800 A against DIN 750, or 0.94 per amp, which sits with the rest of the range. The table carries the current guide.
DIN or SAE? They are two test standards for the same thing. In the US a battery’s label usually carries the SAE figure, so read the SAE column when you are in a marine store.
Sideshift
Sideshift makes the same point without a table. Their FAQ puts it first: “The most important consideration is meeting the required cold cranking amperes (CCA).”
The same FAQ asks for
850 A of A battery built to deliver a large current for a few seconds, the kind that starts an engine. Many thin plates suit a thruster’s short, hard burst. on the
Sideshift SS230 Bow Thruster, battery rule The maker’s own listing, read 28 August 2026.
Sideshift HB340 Retractable Houseboat Thruster, battery rule The maker’s own listing, read 30 August 2026.
Sideshift SS350 Bow Thruster, battery rule The maker’s own listing, read 28 August 2026.
VETUS
VETUS prints a floor and a ceiling for each model:
| Model | Volts | Batteries | Minimum | Maximum |
|---|---|---|---|---|
| VETUS Bow 45, BOW4512D, battery capacity
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 1 | CCA 625 A | CCA 1250 A |
| VETUS Bow 55, BOW5512D, battery capacity
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 12 | 1 | CCA 625 A | CCA 1250 A |
| VETUS Bow 55, BOW5524D, battery capacity
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 24 | 2 | CCA 342 A | CCA 683 A |
Three things in that table matter beyond the numbers.
The first is the unit. VETUS sells its own marine batteries in 9 sizes (55 to 225 Ah), yet the table is in cranking amps.
The second is that the figures have moved. The December 2019 revision of the BOW55 manual printed an amp-hour figure beside every cranking figure, from 85 to 200 Ah for the 12 V model. It asked for 700 CCA.
The May 2026 revision asks for 625. For the 24 V model it asked 500 and now asks 342. The amp-hour column is gone.
The third is that there is a maximum. The manual gives the reason: “If significantly larger batteries in combination with very short battery cables of significantly larger diameter than recommended are used then the thrust will increase. In such cases the maximum length of usage must be reduced in order to prevent damage to the motor.” (VETUS BOW45D manual).
A bigger battery on a shorter, fatter cable makes a stronger thruster. A stronger thruster with the same motor runs hotter. So the maximum is a duty limit.
Where the bank lives, and what a long cable costs
Sleipner, VETUS and Sideshift all want the battery near the thruster, and they say it plainly. VETUS puts it this way: “We also recommend that each bow thruster is powered by its own separate battery or batteries. This allows the battery bank to be placed as close as possible to the bow thruster; the main power cables can then be short thus preventing voltage losses caused by long cables.”
Sideshift gives a distance: “Batteries should be installed as close as possible to the thruster, and not more than thirty feet from the motor controller.”
Sleipner’s FAQ recommends “a separate battery bank (that is not lithium) without a Battery Management System” (Sleipner FAQ).
What the distance costs
Here is the cost, on the wiring page’s arithmetic. Take the SE100/185T at 12 volts, drawing 740 A. It runs on the 3/0 American wire gauge, the size scale for electrical cable. The number falls as the cable gets thicker: 2 AWG is thicker than 6, and 1/0, 2/0, 3/0 and 4/0 are thicker still. cable Sleipner specifies for a short run.
Battery 5 feet from the thruster. That is a 10 foot round trip. The cable drops about 4%, and the motor sees about 11.5 V.
Battery 20 feet aft in the engine room. That is a 40 foot round trip on the same cable. The drop is about 15%, and the motor sees about 10.2 V.
Sleipner prints its lower thrust figure at 10.5 volts. So the long run has already spent more than the whole sag allowance in the cable before the battery has sagged at all.
Bigger cable, or a closer battery
Bigger cable closes the gap. By The volts lost in the cable between the battery and the motor. A long or thin cable loses more, and the motor only ever sees what is left. alone, the 5 foot bank holds The American Boat and Yacht Council, the body that writes the standards US boats are built and wired to. A surveyor or an insurer who asks whether wiring is to standard means ABYC’s.’s 10 percent allowance on 2 AWG, lighter than the 3/0 AWG Sleipner specifies. The 20 foot bank needs 2 x 2/0 AWG.
Those two sizes are by voltage drop alone. ABYC’s E-11 standard also sizes a cable by its The most current a cable can carry all day without overheating, as the standards table it. It depends on the size of the copper and how hot the space it runs through is. table and takes the larger of the two. The wiring calculator applies both.
- The wiring page gives the gauge for every distance.
- The wiring calculator gives it for your run, and the volts the cable already fitted is taking.
- The battery calculator gives the bank each maker asks for and checks yours against it.
Or put the battery where the makers tell you to. Then you run a small charging lead aft instead of a large power lead forward. That is the makers’ whole argument for a bank in the bow.
The windlass exception
Sideshift allows one exception, in its own words: “Only the SS230 may use a windlass battery as a power source. If the boat has a windlass and the cabling is 1/0 in size, and the battery meets the recommended type and CCA requirements” (Sideshift FAQ).
A The electric winch at the bow that raises the anchor. It has its own heavy cable and often its own battery. That is why a bow thruster is sometimes wired alongside it. battery already lives in the bow. It already meets a cranking spec and is already wired heavy. If yours does, the smallest Sideshift can share it. Sideshift allows it for no other series.
A battery beside the thruster has to be sealed. VETUS adds this safety condition: “Be sure to only use ‘sealed’ batteries if the batteries are located in the same compartment as the bow thruster.”
A thruster motor has Small carbon blocks inside a motor that press on the spinning part and carry the current into it. They wear down, they shed dust, and they are the usual reason an old thruster motor stops., and brushes spark. A flooded battery on charge gives off hydrogen. If they share a locker, the battery has to be sealed.
Mounting a battery at the bow: what ABYC asks
A bank at the bow is a new battery installation, and ABYC's battery standard, E-10 (July 2021 edition), sets the rules for it. There are six to know.
- Tie it down. The battery may move no more than an inch in any direction under a pull of twice its own weight: up, fore and aft, and side to side.
- Keep it off the fuel. It may not sit directly above or below a fuel tank, fuel filter or fuel line fitting without a deck or floor between. Metal fuel parts within 12 inches of the terminals get a nonconducting shield.
- Cover the positive terminal. Use a boot, a covered nonconducting box, or a compartment built for the battery alone.
- Vent it. The rule covers sealed, AGM and gel batteries too. A box whose lid forms a pocket over the battery is vented at the top.
- Make the connections properly. No wing nuts on cable of 6 AWG or larger. At most four cable ends go on one post, the heaviest cable next to the battery. No spring clips or temporary clamps.
- Fit a battery switch. E-11 (July 2025 edition) asks for one in the positive cable of every battery or bank over 800 CCA, or over 100 amp-hours where no CCA is given.
E-10 also defines the rating the makers use. A battery's CCA is the current it delivers for 30 seconds at 0 F while holding 7.2 volts on a 12 volt battery. Checking your install against the standards is yours, or your surveyor's.
Starting, deep cycle, AGM, lithium: what the makers say
What matters to the thruster is the voltage the battery holds while 740 A leaves it. Each chemistry answers that differently. Here are the makers’ positions, verbatim.
Sleipner, on battery types. It recommends “lead-acid, AGM, gel, or similar kinds of batteries”. For its on/off DC models it wants a bank without a Battery management system: the electronics inside a lithium battery that protect it by cutting the connection when something looks wrong. A thruster’s sudden heavy draw can look wrong to it.. The reason: “thrusters draw a lot of currents quickly, and the high amp draw may lead the BMS system to think that there is an issue”, and the BMS disconnects.
Sleipner, on lithium with on/off models. Its FAQ explains the difference: “Lithium or Li-ion battery may maintain a significantly higher voltage and higher current under load than a lead-acid, gel or AGM battery”. As a result the “propeller will rotate significantly faster”, and the risk of Bubbles forming on a propeller blade when it is working too hard or running too near the surface. The propeller spins and the push disappears. and damage rises.
Sleipner, on lithium with proportional models. Here the answer is the opposite: “All Sleipner proportional thrusters will work well with Li-ion or LiFePO4 batteries”
Sleipner, for every model. Its advice is short: “Always make sure you measure your voltage on the thruster” (Sleipner FAQ).
Sideshift specifies a starting type, “NOT deep cycle”, on every series. On using the house bank, it says: “We don’t recommend deep cycle batteries for our thrusters. However, if the correct cold cranking amps (CCA) is present this may be an option.” (Sideshift FAQ).
VETUS names its own sealed maintenance-free SMF and Absorbed glass mat: a sealed lead-acid battery with the acid held in fiberglass matting. It gives off no gas in normal use and holds its voltage well under a heavy draw. That is why thruster makers name it. batteries as ideally suited. It requires a sealed type in a shared compartment. For the on/off range it publishes no lithium guidance we could find.
VETUS BOW PRO, the proportional range, runs in a stated window: 10.5 to 14.4 volts on a 12 volt system, and 21 to 28.8 on 24 (BOW PRO manual).
Put together, the makers agree on the on/off units. Each one sizes them in cranking amps around a lead-acid or AGM type battery, and none of them names a A battery built to be drained slowly and recharged many times, the kind that runs the lights and the fridge. Its thick plates last through many cycles, but they give up current slowly, where a thruster asks for a lot of it at once. The batteries that run the boat’s lights, fridge and electronics, as distinct from the engine’s starting battery. They are built for a slow, steady draw. as the fit. Sideshift names a A battery built to deliver a large current for a few seconds, the kind that starts an engine. Many thin plates suit a thruster’s short, hard burst. and advises against deep cycle outright.
Lithium is the open question. The answer depends on whether the thruster has a controller between the battery and the motor.
Sleipner gives the mechanism. Lithium holds its voltage up under load, which is what makes it attractive. On a motor with no controller, that higher voltage spins the propeller faster than the tunnel was designed for. On a proportional unit the controller holds the thrust steady, and the same property buys run time.
ABYC's lithium standard, E-13 (July 2025 edition), covers any lithium system over 500 watt-hours. It gives three rules that bear on a thruster.
ABYC requires a battery management system that can cut the battery off (section 13.6.1.1). That is the part Sleipner warns may read a thruster's draw as a fault.
ABYC recommends a second power source for critical systems, propulsion among them, in case the management system shuts the battery down.
Each lithium battery or bank gets a switch of its own, apart from the management system's cutoff (section 13.6.7.1). The battery maker's instructions govern the rest of the install.
Thinking about lithium? Ask the maker about your model before you buy. Once it is in, measure the voltage at the motor.
Twelve volts or twenty-four
Sleipner sells several models at both voltages and prints a battery for each. So the difference can be read straight off the manuals:
| Model | Draw at 12 V | Min CCA at 12 V | Draw at 24 V | Min CCA at 24 V |
|---|---|---|---|---|
| Sleipner Side-Power SE60/185S, 12 V against 24 V
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 370 A | 350 A | 170 A | 175 A |
| Sleipner Side-Power SE80/185T, 12 V against 24 V
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SE100/185T, 12 V against 24 V
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SE130/250T, 12 V against 24 V
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 800 A | 750 A | 350 A | 400 A |
| Sleipner Side-Power SEP60/185S, 12 V against 24 V
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 370 A | 350 A | 170 A | 175 A |
| Sleipner Side-Power SEP80/185T-IP, 12 V against 24 V
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SEP80/185T, 12 V against 24 V
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SEP100/185T, 12 V against 24 V
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SEP100/185T-IP, 12 V against 24 V
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SEP60/185S-IP, 12 V against 24 V
Defender listing, read 12 October 2026. Full page: fit, cost and wiring See it on Defender | 370 A | 350 A | 170 A | 175 A |
| Sleipner Side-Power SE60/185S-IP, 12 V against 24 V
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 370 A | 350 A | 170 A | 175 A |
| Sleipner Side-Power SE80/185T-IP, 12 V against 24 V
Defender listing, read 17 September 2026. Full page: fit, cost and wiring See it on Defender | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SE100/185T-IP, 12 V against 24 V
Defender listing, read 28 August 2026. Full page: fit, cost and wiring See it on Defender | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SX80, 12 V against 24 V
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SX100, 12 V against 24 V
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SXP80 PRO, 12 V against 24 V
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SXP100 PRO, 12 V against 24 V
A dealer’s listing, read 14 October 2026. Full page: fit, cost and wiring See it at the dealer | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SRL80, 12 V against 24 V
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SRL100, 12 V against 24 V
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SRP80 PRO, 12 V against 24 V
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SRLP100 PRO, 12 V against 24 V
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SRVP80 PRO, 12 V against 24 V
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 530 A | 550 A | 280 A | 300 A |
| Sleipner Side-Power SRVP100 PRO, 12 V against 24 V
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 740 A | 750 A | 340 A | 400 A |
| Sleipner Side-Power SRL130, 12 V against 24 V
The maker’s own listing, read 15 October 2026. Full page: fit, cost and wiring See it on the maker’s site | 800 A | 750 A | 350 A | 400 A |
| Sleipner Side-Power SRV130, 12 V against 24 V
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 800 A | 750 A | 350 A | 400 A |
| Sleipner Side-Power SEP50/140S, 12 V against 24 V
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 370 A | 350 A | 170 A | 175 A |
| Sleipner Side-Power SEP50/140S-IP, 12 V against 24 V
A dealer’s listing, read 15 October 2026. Full page: fit, cost and wiring See it at the dealer | 370 A | 350 A | 170 A | 175 A |
Twenty-four volts roughly halves the current. That means a smaller cranking figure, a thinner cable, and less lost in the run.
What it costs is a second battery. A 24 volt bank is two 12 volt batteries Batteries joined end to end, the positive of one to the negative of the next. The voltages add, so two 12 volt batteries make a 24 volt bank, and the cranking figure does not add.. That is how Sideshift specifies its 350 series (two 12 V batteries in series, for 24 V). You also need a charging arrangement that suits a 24 volt bank on a boat that is otherwise 12.
The copper side of the same choice is worked through on the wiring page.
Charging a bank that lives in the bow
A dedicated bank forward needs something to charge it. The thruster takes a lot out in a short burst and then sits idle for hours. That is a A battery built to deliver a large current for a few seconds, the kind that starts an engine. Many thin plates suit a thruster’s short, hard burst.’s life.
The charging path is the small lead that replaces the large one. There are two ways to do it. The first is a charger circuit from shore power. The second is a feed from the house system that only has to carry charging current.
The makers say less about charging than about anything else on this page. Max Power and Sideshift name a charger or a feed. VETUS builds a charger into its BOW PRO Boosted units. ezDrive and Yacht Thruster wire the unit to the boat’s own supply. Sleipner Side-Power, Quick and Lewmar say nothing about it. Here is each maker’s position, from the document named beside it.
- Sleipner Side-Power. The word "charging" is not in any of the Sleipner guides we read. The battery is sized by cold cranking amps, and a battery near the thruster is suggested. How it gets charged is left to you and your installer. (SE80 to SE150 installation guide, document 2687 rev 30, page 19).
- VETUS. Every VETUS manual wants "its own separate battery or batteries" near the thruster, sealed if it shares the motor's compartment. The BOW PRO Boosted units carry a charger (12 V, 80 A) fed from the boat's bank, with a fused feed cable. The other manuals show an alternator and a battery separator on the wiring diagram and say nothing more. (BOW55D installation manual 020522.11 r08 and the BOW PRO Boosted manual 020808.04 r09, page 22 of the Boosted manual).
- Max Power. Max Power is the one maker that asks for both: the engine's alternator and a charger. A dedicated bank is optional and goes "as close as possible to the thruster". It wants starting-type batteries with high cold cranking amps. (CT100 and CT125 installation manual, page 3).
- Quick. The manual gives a battery table by model, in amp-hours and cold cranking amps, and a diagram with the panel on the service battery. It says nothing about how the thruster bank is charged. (BTQ Series installation manual REV 005A and the TCD control manual, page 10).
- Lewmar. The manual sizes the battery by cranking amps and says to "ensure batteries are fully charged before switching on the main power". It gives no rule on a charger, a feed or a bank of its own. (Gen 2 TT installation manual 559231 and the RT manual 55110070, page 12).
- Sideshift. The thruster gets a bank of its own: cranking type, 850 cold cranking amps per battery, within 10 ft of the controller. You buy the charger too, either a shore charger or a DC-to-DC charger fed off the bank the alternator charges. (Monohull installation manual Rev 3.1, page 40).
- ezDrive. It wires straight to a 12 V battery, and ezDrive suggests a Group 31 AGM of its own. The guide says nothing about a charger. (Streamline installation guide and the FAQ, page 2).
- Yacht Thruster. A 12 V unit may share the boat's supply, even a windlass feed if a specialist agrees. A 24 V unit on a 12 V boat needs a bank of its own. Neither page names a charger. (Overview and FAQ pages, from the FAQ).
The cost page’s parts list prices the chargers one dealer sells and says which line of an estimate holds them.
The one itemized job we hold is a houseboat from December 2016. It put the charger at $225 against a $2,500 bank.
Self-contained units
The self-contained units sidestep the question. A DockStar carries its own 12.8 volt, 15 Ah lithium battery and ships with a charger for a household outlet.
That gives about 10 minutes of run per charge, which is many dockings. Recharging takes about 5 hours from empty, so plan on shore power or an inverter.
The charger is an AC unit on a cord that plugs into a 110 volt outlet. You can charge the thruster where it sits on its rail, as long as no water gets into the charger or the charger port. The manual says to keep the port covered with its plug when you are not charging. You can also take the thruster off the rail and charge it somewhere dry.
That is the whole electrical installation. It is why the DIY page prices its wiring line at nothing.
What the battery line costs
Every product page now counts the batteries, cable and charger for its own unit: how many 12 V batteries the bank takes, each at the maker’s own minimum, the maker’s cable for a bank close to the thruster, and a charger, at a dealer’s prices. Across the tunnel units that comes to $483–$4,767: one small battery at the low end, four big ones in series at the top.
Owner reports put the line at $1,000–$1,400 on a typical 35 to 40 foot job, and the cost page’s worked example still uses that.
The one itemized breakdown we hold shows why it is the line to watch. On the December 2016 houseboat job the electrical came to $3,025. Of that, $2,500 was the battery bank.
The electrical was 75% of the $4,025 in itemized lines. The tube and the welding were the cheap part. It was a welded aluminum hull at December 2016 prices, one example, and your own boat will price differently.
This is also the line an owner can take on. Experienced owners buy the battery, run the cable and fit the charger while the yard does the hole. The DIY page works out what that is worth.
Sideshift’s own figure for its externals is lower. The DIY page’s fixed-mount external row carries it.
What each maker publishes, and what none does
Sleipner, VETUS and Sideshift fill the tables on this page. Here is what each maker’s documents give.
Sleipner Side-Power. A stated draw, a minimum battery in cold cranking amps, a thrust figure at the sagged voltage, and an FAQ that explains its lithium position.
VETUS. A minimum and a maximum per model in cranking amps (the 2019 revision also gave amp-hours). It also gives the separate-battery recommendation, the sealed-battery rule, and a reason for the maximum. This page carries 3 models. The wiring page carries the rest of the range's table.
Sideshift. A cranking figure per series, a battery type, a distance, and a windlass rule. For charging it names a shore charger or a DC-to-DC charger.
Lewmar. Its Gen 2 manual gives a stated current per model. It gives one sentence for the bank: battery cranking capacity "should be at least equal to the thruster current" (our Lewmar review).
Quick. Its BTQ manual gives a fuse and a cable cross-section per model and no battery figure at all (our Quick review).
Max Power. Its manuals give a total cranking figure for 26 of its 41 models in the battery calculator, and an example battery for the other 15. The battery calculator carries them; this page does not.
Every figure above is the maker’s own number, or our arithmetic on one, with the number it came from beside it.