Battery Run Time Estimator
Battery run time from mAh and mA at one voltage, or from Wh and watts, times an efficiency you set for converter losses. Shows hours, minutes and Wh. How it works
Use the Battery Run Time Estimator
About the Battery Run Time Estimator
A 3000 mAh battery at 3.7 V feeding a 500 mA load runs 5 hours 6 minutes at the default 85% efficiency: 11.1 Wh ÷ 1.85 W = 6 hours before losses, and 6 × 0.85 = 5.1 hours. The battery run time estimator works from mAh, volts and mA, or directly from Wh and watts.
Runtime of a 3000 mAh, 3.7 V battery at different loads (85% efficiency)
| Current draw | Power | Runtime | Hours | Hours before efficiency |
|---|---|---|---|---|
| 50 mA | 0.19 W | 51h 0m 0s | 51 h | 60 h |
| 100 mA | 0.37 W | 25h 30m 0s | 25.5 h | 30 h |
| 250 mA | 0.93 W | 10h 12m 0s | 10.2 h | 12 h |
| 500 mA | 1.85 W | 5h 6m 0s | 5.1 h | 6 h |
| 1000 mA | 3.7 W | 2h 33m 0s | 2.55 h | 3 h |
| 2000 mA | 7.4 W | 1h 16m 30s | 1.27 h | 1.5 h |
Energy is 11.1 Wh in every row. Power is rounded to two decimals as the page shows it; the runtime is computed from the unrounded values. The 500 mA row is the default.
Runtime at a 500 mA load by battery capacity (3.7 V, 85% efficiency)
| Capacity | Energy | Runtime | Hours |
|---|---|---|---|
| 1,000 mAh | 3.7 Wh | 1h 42m 0s | 1.7 h |
| 2,000 mAh | 7.4 Wh | 3h 24m 0s | 3.4 h |
| 3,000 mAh | 11.1 Wh | 5h 6m 0s | 5.1 h |
| 4,000 mAh | 14.8 Wh | 6h 48m 0s | 6.8 h |
| 5,000 mAh | 18.5 Wh | 8h 30m 0s | 8.5 h |
| 10,000 mAh | 37 Wh | 17h 0m 0s | 17 h |
Runtime is proportional to capacity at a fixed load.
Wh mode: a 50 Wh battery at different power draws (85% efficiency)
| Power draw | Runtime | Hours | Hours before efficiency |
|---|---|---|---|
| 5 W | 8h 30m 0s | 8.5 h | 10 h |
| 10 W | 4h 15m 0s | 4.25 h | 5 h |
| 25 W | 1h 42m 0s | 1.7 h | 2 h |
| 50 W | 0h 51m 0s | 0.85 h | 1 h |
In Wh mode the voltage is not needed.
How to use this tool
- Choose mAh or Wh mode.
- Enter the capacity, the load (mA in mAh mode, W in Wh mode) and, in mAh mode, the battery voltage.
- Set the system efficiency from 1 to 100%, then read the runtime in hours, minutes and seconds.
Frequently asked questions
- How long will a 3000 mAh battery last at 500 mA?
- 5h 6m 0s (5.1 hours) at the default 85% efficiency, with a 3.7 V battery. With no losses, at 100% efficiency, it is 6h 0m 0s, and at 70% it is 4h 12m 0s.
- How do I convert mAh to Wh?
- Multiply the mAh by the battery voltage and divide by 1000. 3000 mAh at 3.7 V is 11.1 Wh, and 5,000 mAh at 3.7 V is 18.5 Wh.
- What efficiency should I enter?
- The page gives no measured figure for your device: efficiency is your input, 85% to start. Use 100% to ignore all losses, or a lower figure to cover converter, regulator and heat losses. The runtime scales directly with it: 85% gives 5.1 hours where 100% gives 6. Efficiency is not the place for charge you cannot use: if the device shuts off before the battery is flat, or you want to keep a reserve, enter a smaller capacity instead.
- Does the battery voltage change the runtime?
- Not in mAh mode. The tool uses one voltage for the battery and the load, so it cancels out: 2000 mAh at 200 mA runs 8h 30m 0s at 85% whether you enter 1.2 V or 4.8 V. Only the energy and power figures change, 2.4 Wh and 0.24 W against 9.6 Wh and 0.96 W. When a converter runs the load at another voltage, such as a 5 V USB device on a 3.7 V cell, use the Battery Life Calculator, which takes both voltages.
- How long will a 50 Wh battery run a 10 W load?
- In Wh mode that is 4h 15m 0s (4.25 hours) at 85% efficiency, or 5 hours before losses.
- Why does my real battery last a different time?
- The tool treats the capacity as one fixed number and the load as steady. A rated mAh figure is measured at a particular discharge current, and manufacturer data sheets such as Energizer’s for its E91 AA cell chart the capacity at several currents.
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