Estimates how long a device runs from its battery capacity and voltage and its power draw. A rating in mAh is current times time, so it only becomes energy in watt-hours once multiplied by the voltage — capacity alone cannot be compared across devices.
This tool estimates how long a device will run, from the capacity and voltage of its battery and the power it draws.
Here is the capacity in mAh, the voltage, the energy in watt-hours, the power draw in watts and the run time in hours.
Milliamp-hours are current multiplied by time, which measures charge rather than energy. Energy appears only once the voltage is brought in.
That is why a figure in mAh cannot be compared across devices. Five thousand mAh at 3.7 V is 18.5 Wh, while the same 5000 mAh at 11.1 V is 55.5 Wh, three times the energy. It is also why power banks are increasingly labelled in watt-hours as well.
A 5000 mAh battery at 3.7 V, driving a device that draws 2.5 W, lasts 7.4 hours, or 7 hours 24 minutes.
Five thousand mAh is 5 Ah. Multiplying by 3.7 V gives 18.5 Wh, and dividing by 2.5 W gives 7.4 hours.
Real run times fall short of this. Around a tenth is lost converting the voltage, a cell stops before it is fully drained because its voltage sags, and in the cold the recoverable charge itself drops. Treat the figure as a rough ceiling.
Where the draw varies, enter the average power rather than the peak.