Battery Life Calculator
Estimate how long a battery will last from its capacity and the device's power draw.
Runtime from capacity and draw
Roughly, how long a battery lasts is its capacity divided by how much power the device draws — a bigger battery or a lower draw runs longer. This estimates runtime from those figures, so you can tell how long a device will keep going between charges.
Enter the battery capacity and the device's current draw to see the estimate.
Why real runtime is shorter
The simple division gives an optimistic ceiling, and real battery life is usually somewhat less for a few reasons. No battery delivers its full rated capacity in practice, especially as it ages and its capacity fades over hundreds of charge cycles. Higher current draws are less efficient, and cold temperatures cut capacity noticeably. Devices also rarely draw a constant amount — a phone sips when idle and gulps under load. So treat the calculated figure as a best case.
Common questions
Why does my battery last less than calculated?
Batteries do not deliver full rated capacity in practice, fade with age, and lose capacity in the cold, so real runtime is a bit shorter.
What do I need to estimate runtime?
The battery capacity and the device's current draw — runtime is roughly capacity divided by draw, treated as a best case.
Is anything uploaded?
No. The calculation happens in your browser.