To size a trolling motor battery, multiply the current your motor draws at the speed you usually run by the hours you want to fish, then add margin. For example, a motor averaging 20 amps for 5 hours needs about 100 amp hours of usable capacity. Lead-acid and AGM batteries should not be regularly drained below about half, so they need roughly twice the rated capacity; lithium (LiFePO4) batteries can use most of their rated capacity. Most anglers with a 12V motor use one battery of about 100Ah; 24V and 36V motors use two or three batteries of the same size in series.
How many amp hours does a trolling motor use?
It depends almost entirely on speed. At full throttle a trolling motor draws its maximum current, which is listed in its manual, while at the slow speeds most anglers use it draws a fraction of that. Wind, current and GPS anchoring raise the average, because the motor works harder to hold position. Check your motor’s specified maximum amp draw, and use a battery monitor to learn your real average.
A simple sizing method
- Estimate your average current draw in amps at your usual speeds.
- Multiply by the hours you fish in a day.
- For lead-acid or AGM, double the result; for lithium, add about 20 percent margin.
- Round up to the next common battery size.
24V and 36V systems
Wiring batteries in series adds voltage, not amp hours. Two 12V 100Ah batteries in series give 24V at 100Ah, and three give 36V at 100Ah. Each battery in a series bank should be the same type, capacity and age. Higher-voltage motors draw less current for the same power, so run time per amp hour improves. See 12V vs 24V trolling motors, 24V vs 36V and how to wire a 24 volt trolling motor.
Lithium vs lead-acid for capacity
Because lithium can be drained deeper and holds its voltage, a 100Ah lithium battery gives close to twice the usable energy of a 100Ah lead-acid battery, at about half the weight. It costs more up front but lasts many more cycles. See lithium vs lead-acid trolling batteries and how long lithium batteries last.
Don’t forget the charger and wiring
A larger bank takes longer to charge, so match your charger to the battery type and capacity; see lithium battery chargers. Use the wire size and circuit breaker the motor maker specifies; see trolling motor wiring.
Batteries we list
- LBP Lithium Battery Bundles (12V 100Ah or 36V 60Ah LiFePO4 with onboard charger and tray): $970.00
- Ionic Lithium 12V 300Ah LiFePO4 with Bluetooth and heater: $1,599.00
For run time on a battery you already have, see how long a trolling motor battery lasts.
More guides: LiFePO4 vs lithium-ion.
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