How far into a fishing day does your trolling motor battery last? That depends on thrust setting, water conditions, and battery type — not just the amp-hour rating stamped on the case. This calculator estimates marine battery runtime for trolling motors and onboard electronics so you can plan your day on the water without getting stranded.
Trolling Motor Power Draw by Thrust
| Motor Thrust | System Voltage | Speed 3 (Amps) | Speed 3 (Watts) | Max Speed (Amps) | Max Speed (Watts) |
|---|---|---|---|---|---|
| 30 lbs | 12V | 10A | 120W | 30A | 360W |
| 55 lbs | 12V | 15A | 180W | 40A | 480W |
| 70 lbs | 24V | 12A | 288W | 42A | 1,008W |
| 80 lbs | 24V | 14A | 336W | 50A | 1,200W |
| 112 lbs | 36V | 15A | 540W | 50A | 1,800W |
Most anglers run at speed 3-5 for positioning, not at full throttle. At medium speed, a 55lb thrust 12V motor draws roughly 15-20A. That is 180-240W — far less than the maximum 480W.
Example: A Full Day Bass Fishing
Setup: 12V 100Ah deep cycle AGM battery. 55lb thrust trolling motor. Fish finder (20W). Livewell pump (40W, runs 25% of the time = 10W average).
You fish for 6 hours. The trolling motor runs at medium speed (speed 4, about 18A = 216W) for roughly 40% of the time — you are drifting, anchored, or using the main motor the rest. Average trolling motor draw over the day: 216 x 0.40 = 86W.
Total average load: 86 + 20 + 10 = 116W. Battery energy at 50% DoD and 95% efficiency: 100 x 12 x 0.50 x 0.95 = 570Wh.
Runtime: 570 / 116 = 4.9 hours. That is tight for a 6-hour day. You would need to cut back on trolling motor use, bring a second battery, or upgrade to a 150Ah battery to have comfortable margin.
Frequently Asked Questions
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Marine battery runtime is more variable than any other application because water conditions change constantly. Size your battery for the worst day you expect on the water, not the average day. Coming back to the dock with 30% battery left is a good trip — coming back under tow because the trolling motor died is not.
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Written and maintained by Dan Dadovic, Developer & Off-Grid Energy Enthusiast. On the energy side, Dan has hands-on experience with residential solar panel installation, DIY battery bank construction, off-grid power systems, and wind power — all from building and maintaining his own systems..
Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.