Trolling Motor Battery Runtime Calculator
Estimate trolling motor battery runtime from amp-hour capacity and thrust level.
Covers 12V and 24V setups at four common speed settings.
A trolling motor draws current proportional to the thrust it produces. At full throttle, a 55 lb thrust motor on 12V pulls roughly 50 amps. Drop to 50% speed and current falls to around 20 amps — not half, because thrust is non-linear with power.
Runtime = (battery capacity × 0.8) / amp draw
The 0.8 factor is the safe discharge limit for lead-acid batteries. Running below 20% state of charge (below about 11.8V on a 12V battery) degrades the battery noticeably. Lithium batteries tolerate deeper discharge but cost more upfront.
Typical amp draw by thrust and speed setting:
- 30 lb thrust: 30A full, 18A at 70%, 12A at 50%, 7A at 30%
- 55 lb thrust: 50A full, 30A at 70%, 20A at 50%, 12A at 30%
- 80 lb thrust: 56A full, 34A at 70%, 22A at 50%, 13A at 30%
Most anglers spend the majority of time at 30–50% throttle while positioning, with brief bursts to move spots. For trip planning, 50% average throttle gives a reasonable estimate.
Battery capacity drops in cold weather. A 100 Ah battery rated at 77°F loses roughly 20% at 32°F. If you fish in winter, build in that margin.
Two batteries in parallel doubles your amp-hours. Running a 24V system instead of 12V on the same bank cuts amp draw roughly in half — 24V motors are significantly more efficient for larger boats.
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