How long a trolling motor battery lasts on the water depends on two things: how much usable energy the battery holds and how much current the motor draws at the speed you run. A rough estimate is usable amp-hours divided by amp draw. At low speeds a 12-volt motor may draw well under 10 amps, while flat out it can draw 40 to 50 amps or more, so the same battery can last anywhere from about an hour to a full day.
A simple run-time estimate
- Find the battery’s amp-hour (Ah) rating.
- Work out usable capacity: lead-acid batteries should be kept above about 50 percent charge, so a 100 Ah lead-acid battery offers about 50 Ah; lithium batteries can use most of their rating.
- Find the motor’s amp draw at your usual speed from the manufacturer’s chart.
- Divide usable Ah by amps: 50 Ah at 10 amps is about 5 hours; at 25 amps, about 2 hours.
Wind, current, boat weight and a fouled prop all raise the draw.
Typical figures
| Battery | Usable capacity (approx.) | At low draw | At high draw |
|---|---|---|---|
| 100 Ah lead-acid | About 50 Ah | Several hours | About 1 to 2 hours |
| 100 Ah lithium | About 80 to 100 Ah | Most of a day | About 2 to 3 hours |
These are illustrations; real results depend on the motor and conditions.
Why lithium changes the math
Lithium batteries hold their voltage almost to the end of their charge, so the motor keeps its speed instead of slowing as the battery drains, and they weigh far less than lead-acid batteries of the same capacity. They cost more up front but usually last many more cycles; see our 12V 300Ah LiFePO4 battery ($1,599.00).
On a kayak
Kayak motors are usually small and run at low speed, so a modest lithium battery can last a long day, and weight savings matter most. Size the battery to your typical trip with a margin.
How many years do trolling motor batteries last?
Lead-acid deep-cycle batteries commonly last a few seasons with good charging habits, while lithium batteries are rated for many more charge cycles; see how long do lithium batteries last? Deep discharges and leaving batteries flat shorten life most.
Getting more run time
- Run at the lowest speed that does the job; draw rises steeply near full speed.
- Keep the prop clean and undamaged; see trolling motor prop.
- Use a higher-voltage system with more batteries for bigger boats; see 12V, 24V and 36V batteries.
- Charge fully after every trip; see how to charge a trolling motor battery.
GPS anchoring in wind can draw a lot of current, so plan extra capacity if you use Spot-Lock often; see Spot-Lock trolling motors and the trolling motor size guide.
More guides: lithium vs lead-acid · deep cycle vs starting battery · how much power Spot-Lock uses · brushless vs brushed run time · how fast a trolling motor goes · 12V vs 24V run time · lithium battery chargers · trolling motor wiring · how deep a trolling motor should be · how long trolling motors last · how many amp hours you need for a trolling motor.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.