Trolling motor battery: 12V, 24V or 36V, wired right

The short answer. Match the battery to your motor’s voltage: 12V takes one battery, 24V takes two in series, 36V takes three. Or use one lithium battery built at 24V or 36V. Put a breaker on the positive near the battery, size the wire for the run, and never run the motor off your engine’s start battery.

You’ll need

• Your trolling motor’s voltage and max amp draw (it’s in the manual and in the table below)
• A deep cycle battery, or two or three for 24V or 36V
• A circuit breaker sized for your motor
• Wire sized for the run with the Wire gauge calculator
• A charger that matches your battery: voltage, chemistry and the battery maker’s charge settings

You can do this. Let’s go.

12V, 24V or 36V: which battery setup?

Your motor decides. Check the label or the manual.

Minn Kota’s guidance for a 12V battery: deep cycle, at least 110 Ah, usually a group 27. No Ah rating on the label? Look for at least 180 minutes of reserve capacity.

One battery at 24V or 36V means one case to mount, one set of terminals and no jumpers.

Going 24V or 36V with 12V lithium batteries in series? Only if that battery’s maker allows series. Check its manual first.

How do I wire two or three batteries in series?

From Minn Kota’s steps. Motor off, or speed set to 0, first.

24V (two batteries) 1. Jumper from battery 1 positive (+) to battery 2 negative (-). 2. Motor red lead to battery 2 positive (+). 3. Motor black lead to battery 1 negative (-).

36V (three batteries) 1. Jumper from battery 1 positive (+) to battery 2 negative (-). 2. Jumper from battery 2 positive (+) to battery 3 negative (-). 3. Motor red lead to battery 3 positive (+). 4. Motor black lead to battery 1 negative (-).

Series adds voltage, not run time. Two 100 Ah batteries in series are still 100 Ah, at 24V.

Parallel is the other way: it adds run time at the same voltage. Minn Kota says batteries in parallel must match in make, type, size and age.

Going lithium with one battery? Skip the jumpers. Red to positive, black to negative, breaker in the red lead. Xantrex says its 24V and 36V batteries can’t be wired in series. Up to four can go in parallel for more hours.

How long will a trolling motor battery last?

Pro-Guide’s rule of thumb: divide the battery’s amp hours by the amps you pull.

• 90 Ah at 30 A is about 3 hours (Pro-Guide, 24VM90).
• 115 Ah at 30 A is about 3.8 hours (Pro-Guide, 24VM115).
• 60 Ah at 30 A is 2 hours (our math, same rule).

Real run time depends on speed, wind, current and the cold. Most days you won’t sit at full power. Minn Kota says to expect a typical day of fishing on one charge with the right battery.

Plug your own numbers into the Run time calculator.

What size wire and breaker for a trolling motor?

Minn Kota’s table, for extending the motor’s leads. Length is the distance from the batteries to the motor leads.

The table assumes 105 °C rated wire, no more than two wires bundled together, and no more than a 3% voltage drop at full power. Minn Kota says the max amp draw only happens now and then. It isn’t a continuous rating.

Three rules from Minn Kota:

• Put the breaker (or an inline fuse) on the positive, as close to the battery as you can. With batteries in series, that’s the motor’s red lead, at the last battery’s positive.
• On a QUEST motor, never use a breaker bigger than 60 A.
• Extending more than 25 ft? Have a qualified marine technician do it.

Another brand of motor? Use its own table, or run your numbers in the Wire gauge calculator and the Fuse size calculator. Use tinned marine wire: Marine wire: why tinned, and which size. Crimp it right: Heat-shrink terminals and crimping battery cable.

On a lithium battery, check the fuse’s interrupt rating too. Xantrex asks for 5,000 A or more per 100 Ah of battery. More on that: Fusing a lithium bank: Lynx, MRBF and class T.

Can I run my trolling motor off the start battery?

No. Minn Kota says a starting battery isn’t suitable for an electric trolling motor, and that cranking amp ratings have no bearing on deep cycle performance.

Keep the motor on its own battery or bank. Your start battery stays full for the engine. Its own job, its own charger bank.

How do I charge trolling motor batteries at the dock?

Two or three 12V batteries in series: charge each battery on its own. Minn Kota says its chargers are 12V only, and batteries in series can’t be charged on one bank. Use a charger with one bank per battery. The jumpers can stay on with a Minn Kota charger.

One 24V or 36V lithium battery: use a charger built for that voltage and for lithium, set to the battery maker’s numbers:

Xantrex recommends 25 A of charge current or less, 50 A max, and charging only between 32 °F and 131 °F (0-55 °C). Pro-Guide’s Connect-Ease kits for one-battery 24V and 36V setups come with onboard charging leads and a 60 A breaker.

Before you put any charger on lithium, Minn Kota says to check the battery maker’s charging requirements.

Going lithium? Two checks first

1. Continuous amps. The battery’s continuous current has to cover your motor’s max draw. Pro-Guide’s: 24VM90 90 A, 24VM115 100 A, 36VM60 60 A, 36VM75 75 A. For Xantrex, check its owner’s guide.
2. Brushed motors. Minn Kota says lithium holds a higher voltage for longer, which can be too much for motors built for flooded lead-acid. On those, keep to 85% speed (8.5) or lower. Its QUEST motors are optimized for lithium and also run on deep cycle lead-acid.

Weighing it up? Lithium vs lead-acid batteries for boats, vans and RVs.

Step by step: putting in a trolling motor battery

1. Check the motor. Voltage, max amp draw, and the breaker its maker asks for.
2. Pick the battery. One 12V, two or three in series, or one 24V or 36V lithium.
3. Mount it. Secure, near the motor, so the wire run stays short.
4. Size the wire, then the breaker. Measure from the batteries to the motor leads, then use the table above or the Wire gauge calculator.
5. Breaker on the positive, as close to the battery as you can (on series batteries, at the last battery’s positive). Keep it off while you wire.
6. Series jumpers next, if you have them. Leave the motor leads off.
7. Connect the motor last. Red to the final positive, black to battery 1’s negative.
8. Set up the charger. One bank per 12V battery, or a lithium charger at the maker’s voltage.

That’s it. You’ve got this.

Does this guide fit your boat?

This applies if: – You run a 12V, 24V or 36V trolling motor. – The motor has its own battery or bank.

This doesn’t apply if: – Your trolling motor shares the house bank. That needs its own plan: Upgrading a boat to lithium: everything around the battery. – You’re rewiring the boat’s AC or shore power side. That’s a job for a licensed marine electrician.

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Quick answers

What size battery do I need for a trolling motor? Match the motor’s voltage first. For a 12V motor, Minn Kota suggests a deep cycle battery of at least 110 Ah. More amp hours means more run time.

Can I use one 36V lithium battery instead of three 12V batteries? Yes, if the motor is 36V. Wire red to positive and black to negative, with a breaker on the positive. Charge it with a 36V lithium charger at the battery maker’s voltage.

What size breaker for a trolling motor? Use the motor maker’s size. Minn Kota’s table runs 50 A or 60 A, and says never more than 60 A on a QUEST motor.

Can I charge batteries in series with one charger bank? Not with a 12V charger. Minn Kota says its chargers are 12V only. Charge each battery on its own bank.

Can my trolling motor share the start battery? No. Minn Kota says a starting battery isn’t suitable for a trolling motor.