How to Size a Lithium Battery for a Trolling Motor

Work out the voltage, amp-hours and run time you need, in a few simple steps.

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Step 1: Match the voltage to your motor

Your motor decides the voltage, not the battery. Check the label or manual:

12V motors: usually up to about 55 lb of thrust. They need one 12V battery.
24V motors: usually 70–80 lb of thrust. They need two 12V batteries wired in series or one 24V battery.
36V motors: usually 100 lb of thrust and up, plus electric outboards like the Newport NT300. They need three 12V batteries in series or one 36V battery.

Wiring 12V batteries in series adds their voltage but not their amp-hours. Two 12V 100Ah batteries in series make 24V 100Ah.

Step 2: Find your motor’s amp draw

Amp draw is how fast the motor uses up the battery. Your manual lists the maximum draw at full speed. As a rough guide, 12V motors draw about 30 amps for a 30 lb motor and around 50 amps for a 55 lb motor at full speed. At the lower speeds most people fish at, draw is often a third or less of the maximum.

Step 3: Do the run-time math

Run time (hours) ≈ usable amp-hours ÷ amp draw

Lithium (LiFePO4) batteries can use most of their rated capacity. Lead-acid batteries should only be drained to about 50% to avoid damaging them. That means a 100Ah lithium battery gives you close to double the usable energy of a 100Ah lead-acid battery.

Motor (12V)	Full-speed draw (approx.)	Run time at full speed	Run time cruising (~1/3 draw)
30 lb	~30 A	~3 hours	~9 hours
40 lb	~40 A	~2.25 hours	~6.5 hours
55 lb	~50 A	~1.8 hours	~5.5 hours

Estimates for a 12V 100Ah LiFePO4 battery using 90Ah. Real run time depends on your motor, boat weight, wind and current.

Step 4: Pick the capacity

50Ah: kayaks, short trips and light boats where weight matters most.
100Ah: the common choice for a full day on a 30–55 lb motor.
More than 100Ah, or two batteries: long days, heavy boats, windy water, or running electronics like a fish finder from the same battery.

When in doubt, size up. Running out of power far from the launch is worse than carrying a few extra pounds.

Batteries we compare

12V: LiTime 12V 100Ah Trolling Motor Battery or the compact HQST 12V 100Ah Mini
24V: Redodo 24V 50Ah or Redodo 24V 100Ah
36V: LiTime 36V 50Ah Bluetooth or LiTime 36V 100Ah with charger

See all of them on our marine lithium batteries page.

Don’t forget the charger

Lithium batteries need a charger with a LiFePO4 profile. A standard lead-acid charger may not charge them fully or safely. For a single 12V lithium battery, a dedicated charger like the LiTime 12V 20A Lithium Charger works well. Browse more on our chargers & solar page.

Always add a circuit breaker sized to your motor between the battery and the motor, and use the wire gauge your motor’s manual specifies.

Not sure which motor you need?

Start with our electric boat buying guide or our best trolling motor for a kayak picks.