Battery Life Calculator - Runtime from Capacity, Load & Duty Cycle
Battery Life Calculator
Estimate how long a battery will run your device
Runtime in Plain Time
See the answer as days, hours and minutes, plus the total in hours.
Duty Cycle
Model sensors and gadgets that sleep most of the time by adding the sleep current and the share of time active.
Any Units
Use mAh, Ah or Wh for capacity and mA, A or W for the load; enter the voltage to convert.
Full Privacy
Everything is calculated in your browser.
How Battery Life Is Estimated
The basic rule is runtime = usable capacity ÷ average current. A 2000 mAh battery of which 80% is usable holds 1600 mAh, so a steady 100 mA load runs it for about 16 hours. If the load is on for only part of the time, the average current is the active current times the share of time active, plus the sleep current times the rest, which is how a sensor drawing 50 mA for 5% of the time and 0.01 mA otherwise can last more than three weeks on the same cell.
Real batteries deliver less than their rating when the load is heavy, cold or pulsed, lose capacity as they age and cut out before they are fully empty, so treat the result as an upper-end estimate and lower the usable percentage to be safe. Wh and W figures are converted with the voltage you enter, so use the nominal voltage of the pack, not a fully charged reading.
Key Takeaways
- Sleep current: Ideal for low-power sensors and IoT.
- Usable percentage: Allows for cut-off voltage, age and temperature.
- Optimistic estimate: Real runtime is usually somewhat shorter.