Battery Life Calculator (mAh)
Battery life calculator: how long a battery lasts from its capacity in mAh and the device’s current draw in mA.
t = QI
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
Life (hours) = capacity (mAh) ÷ current (mA). Real batteries deliver about 80–90 % of the label capacity.
Formula
t = QI
| Symbol | Quantity | Units |
|---|---|---|
| Q | Battery capacity | C, mC, µC, nC, e, mAh |
| I | Average current draw | A, mA, µA, kA |
| t | Battery life | s, ms, µs, ns, min, h, d, wk, yr |
Worked example
Given: Q = 3 000 mAh · I = 200 mA
t = QI
Result: t = 15 h
Battery life for different values of Battery capacity
| Q · Battery capacity | t · Battery life |
|---|---|
| 1 500 mAh | 7.5 h |
| 2 250 mAh | 11.25 h |
| 2 700 mAh | 13.5 h |
| 3 000 mAh | 15 h |
| 3 300 mAh | 16.5 h |
| 3 750 mAh | 18.75 h |
| 4 500 mAh | 22.5 h |
| 6 000 mAh | 30 h |
Other values as in the worked example.
Frequently asked questions
3,000 mAh battery at 200 mA?
15 hours (about 12.8 h in practice).
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