Wiring
How to wire a 24 volt trolling motor bank
Quick answer
A 24 volt trolling motor bank is two 12 volt batteries wired in series: positive of the first to negative of the second, with the motor drawing from the two outer terminals. Series wiring doubles voltage at the same amp hours, which is what a motor needs. Parallel wiring instead makes 12 volts at double the amp hours, which will not run a 24 volt motor.
Series and parallel wiring produce two completely different outcomes from the same two batteries, and confusing them is the single most common trolling motor wiring mistake made by owners installing their first multi-battery bank. Series wiring adds the voltages of the batteries together while amp hour capacity stays the same as one battery, which is exactly what a 24 volt motor needs to run at all. Parallel wiring adds the amp hour capacity together while voltage stays the same as one battery, which buys run time on a 12 volt system but produces no 24 volts whatsoever for a motor that requires it.
This guide covers wiring a 24 volt bank specifically: the series connection itself, cable and breaker sizing, and the battery matching rule that protects the investment once the bank is built. The 36 volt version of this same job, with a third battery added, has its own guide linked at the end.
On this page
Series wiring: what it actually does
Series wiring connects the positive terminal of one battery to the negative terminal of the next, chaining them so the two unused outer terminals become the new positive and negative for the whole bank. The published consequence of this connection is straightforward and worth stating plainly because it is exactly backward from what people expect: voltage adds, capacity does not.
Wiring two 100 Ah 12 volt batteries in series produces 24 volts at 100 Ah, while wiring the same two batteries in parallel produces 12 volts at 200 Ah, and only series wiring runs a 24 volt motor.
Published figure A published engineering, regulatory or manufacturer figure. It does not change because somebody disagrees with it.
| Wiring method | Resulting voltage | Resulting capacity | Runs a 24V motor |
|---|---|---|---|
| Series | 24 volts | 100 Ah | Yes |
| Parallel | 12 volts | 200 Ah | No |
This is published battery engineering rather than a rule of thumb. Series adds voltage at the same amp hour rating, parallel adds amp hours at the same voltage.
One 24 volt battery instead of a series pair
A single 24 volt lithium pack such as the LiTime 24V 100Ah replaces the series pair entirely, removing the interconnect cable and the risk of the two batteries in a series pair aging unequally, which over time produces a bank that reads full but underperforms because one battery in the pair has quietly degraded faster than the other. It weighs a fraction of two lead acid batteries combined and delivers close to its full rated capacity at a trolling motor's draw, where Peukert losses hit lead acid far harder. The tradeoff is a higher price up front for one pack versus two separate lead acid batteries.
Sizing the cable for the run
Cable between the two batteries in the series interconnect, and cable from the bank to the motor, both need sizing by voltage drop for the specific run length and current rather than by copying a gauge off a forum thread. Use tinned, finely stranded marine cable such as the End Game marine battery cable, crimp lugs with a proper hex crimper such as the IWISS AP-50BI rather than a hammer and a punch, and seal every connection with adhesive lined heat shrink from a kit like the haisstronica heat shrink connector set. A crimp that looks tight but was not made with a ratchet tool is a connection that will run warm long before it fails outright, and by then it has already cost cycles of the battery's life.
Overcurrent protection on a 24 volt bank
Placement does not change with voltage: overcurrent protection belongs within 7 inches of the battery positive terminal under ABYC E-11, extended to 40 inches when the conductor runs inside a sheath, and everything between the post and the device is unprotected regardless of whether the bank runs at 12, 24 or 36 volts. The Minn Kota MKR-27 at 60 amps is the size Minn Kota publishes for most of its larger 24 volt motors, and the Blue Sea 285-Series 60 amp breaker covers the same size with a resettable switch built in rather than a fuse that has to be replaced after it trips.
Never mix batteries in a series pair
Series wiring only works safely between two batteries of matching chemistry, capacity and age, because a series connection forces the same current through both batteries whether they can handle it equally or not. Never wire a new battery in series with an old one and never wire two different chemistries, such as one AGM and one lithium, into the same series pair. A weaker or different battery in a series pair drags the whole bank's performance down to its own level and can be damaged by the stronger battery pushing it outside its safe operating range during charging.
Wiring a 24 volt trolling motor bank in six steps
- Confirm both batteries match in chemistry, capacity and age. Series wiring only works safely between matched batteries. Replace both together rather than mixing a new battery with an old one.
- Connect the series interconnect. Run a short cable from the positive terminal of the first battery to the negative terminal of the second, using a properly crimped tinned marine cable.
- Identify the new bank positive and negative. The bank's working terminals are the two outer ones left unconnected: the remaining positive on the first battery and the remaining negative on the second.
- Size and run cable to the motor by voltage drop. Calculate the gauge for your specific run length and the motor's published maximum draw rather than assuming a standard size fits every boat.
- Install the breaker within the ABYC E-11 distance. Within 7 inches of the battery positive terminal exposed, or 40 inches sheathed, sized to the manufacturer's published figure where one exists.
- Test voltage at the motor before running it under load. Confirm roughly 24 to 25 volts at the motor's input terminals with a meter before trusting the bank on the water.
Sources
- ABYC E-11 standard for AC and DC electrical systems on boats, overcurrent protection placement
- Minn Kota and LiTime published specifications for the batteries and breakers listed
Frequently asked questions
How do I wire two 12 volt batteries to make 24 volts
Connect the positive terminal of the first battery to the negative terminal of the second with a short cable, which is a series connection. The two remaining outer terminals, the unused positive on the second battery and the unused negative on the first, become the bank's new positive and negative for the motor. This doubles voltage to 24 while keeping capacity the same as a single battery, which is what a 24 volt motor requires.
What is the difference between series and parallel wiring for trolling motor batteries
Series wiring adds battery voltages together while amp hour capacity stays the same as one battery, which is how a 24 or 36 volt motor bank is built. Parallel wiring adds amp hour capacity together while voltage stays the same as one battery, which buys longer run time on a 12 volt system instead. Confusing the two is the classic trolling motor wiring mistake, since parallel wiring will not produce the voltage a 24 volt motor needs at all.
Can I mix an old battery and a new battery in a 24 volt series bank
No. A series connection forces the same current through both batteries regardless of their actual condition, so a weaker or older battery drags the entire bank's performance down and can be damaged by strain from the healthier battery during charging. Replace both batteries in a series pair together when one fails, rather than mixing ages, and never combine two different chemistries such as AGM and lithium in the same series pair.
What size breaker does a 24 volt trolling motor need
Check the manufacturer's published figure first, since Minn Kota specifies 60 amps for most of its larger 24 volt motors through parts like the MKR-27. Where no manufacturer figure exists, size the breaker at least 25 percent above the motor's published continuous draw, then confirm that figure sits at or below the conductor's ampacity for its insulation rating and location under ABYC E-11.
Is a single 24 volt lithium battery better than two 12 volt batteries in series
A single pack such as the LiTime 24V 100Ah removes the series interconnect entirely and avoids the risk of two batteries in a pair aging unequally over time, at a fraction of the weight of two lead acid batteries. It costs more up front than two separate lead acid batteries. Which is better depends on budget, weight priorities and whether the boat already has a lead acid charging system in place.
How do I know if my 24 volt trolling motor bank is wired correctly
Measure voltage at the motor's input terminals with a multimeter before running it under load. A correctly wired series bank of two 12 volt batteries reads roughly 24 to 25 volts at rest. A reading close to 12 volts means the bank is still wired in parallel or the series interconnect was not made, and the motor should not be run until the wiring is corrected.
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Researched, not professional advice. This page is compiled from published engineering and regulatory figures, manufacturer specifications and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are boating convention rather than published standards, and they are labelled that way wherever they appear. Marine electrical work is not house wiring. Use tinned, finely stranded marine cable, size it for voltage drop and for the ABYC E-11 ampacity table rather than one or the other, and put overcurrent protection within seven inches of the battery positive terminal, because everything between the post and the fuse is unprotected. A lithium battery needs a charger with a lithium profile. Never load a boat past its capacity plate, and remember that canoes and kayaks carry no federal capacity plate at all, so their stated capacity is the manufacturer own figure. Wear the life jacket, and treat early season water as the hazard it is: cold water immersion takes your breath and then your hands long before it takes your core.