Battery Life Table: Estimated battery life by Battery capacity
Reference table of estimated battery life for Battery Life across a range of battery capacity values — exact, engine-computed figures you can read off at a glance.
Battery Life Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Estimated battery life
10.50
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Battery Life Calculator
The Battery Life Calculator works out your estimated battery life in an instant. Enter battery capacity, device current draw and efficiency factor and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the battery capacity.
- Enter the device current draw.
- Enter the efficiency factor.
- Read off your estimated battery life — the calculator updates automatically, with no button to press.
Formula
The Battery Life Calculator uses the formula:
Estimated battery life = Battery capacity ÷ Device current draw × Efficiency factor ÷ 100
Worked example
For example, with battery capacity of 3,000 mAh, device current draw of 200 mA and efficiency factor of 7%, the estimated battery life is 10.50.
| Battery capacity | 3,000 mAh |
|---|---|
| Device current draw | 200 mA |
| Efficiency factor | 7% |
| Estimated battery life | 10.50 |
|---|
Results are estimates for educational use, not professional advice.
Frequently asked questions
Divide capacity by the current draw, then apply an efficiency factor. A 3000 mAh battery powering a 200 mA load at 70% efficiency lasts about 10.5 hours.
Real batteries do not deliver their full rated capacity due to heat, voltage drop and conversion losses. 70–85% is a sensible allowance.
Milliamp-hours measure charge capacity. A 3000 mAh battery can in theory supply 3000 mA for one hour, or 300 mA for ten.
Loads vary over time, temperature affects capacity, and ageing reduces it. Treat the result as an estimate, not a guarantee.
The Battery Life Calculator uses the formula: Estimated battery life = Battery capacity ÷ Device current draw × Efficiency factor ÷ 100. For example, with battery capacity of 3,000 mAh, device current draw of 200 mA and efficiency factor of 7%, the estimated battery life is 10.50.
Enter the battery capacity. Enter the device current draw. Enter the efficiency factor. Read off your estimated battery life — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Battery Life: Formula, Steps & Examples
Learn how to calculate Battery Life — the formula explained step by step, with worked examples and a free calculator to check your answer.