Battery Life Calculator
Enter the battery capacity and the average current your device draws. The calculator returns the run time and the energy stored in watt-hours.
Result
- Days and hours
- 0 d 20 h
- Run time in minutes
- 1,200 minutes
- Energy stored
- 7.4 Wh
- Load power
- 0.37 W
Real run time is usually shorter. Capacity falls at high discharge rates, in cold weather and as the battery ages. Use 80 percent usable capacity for a conservative figure.
Formula
- Run time (hours) = capacity (Ah) × usable fraction ÷ load current (A)
- Energy (Wh) = capacity (Ah) × nominal voltage (V)
- 1 Ah = 1,000 mAh
How the Battery Life Calculator works
Battery capacity in amp-hours is the current it can supply multiplied by the time it can supply it. A 2,000 mAh battery delivers 100 mA for 20 hours, or 200 mA for 10 hours, under ideal conditions.
Watt-hours are a better measure for comparing batteries of different voltages, because they describe stored energy. Multiply amp-hours by the nominal voltage.
Worked example
A 2,000 mAh battery powering a 100 mA load lasts 2,000 ÷ 100 = 20 hours. At 3.7 V it stores 2 Ah × 3.7 V = 7.4 Wh.
Frequently asked questions
How long will a 100 Ah battery run a 10 amp load?
Ten hours in theory. For a lead-acid battery discharged only to 50 percent to protect its life, plan on 5 hours.
How do I convert mAh to Wh?
Divide mAh by 1,000 and multiply by the voltage. A 10,000 mAh power bank with 3.7 V cells holds 37 Wh.
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