Battery Life Calculator
Runtime from capacity and current draw.
Enter your values
Results update instantly as you type — no submit needed.
Results
- Runtime
- 13.3 hours
- Runtime in days
- 0.55
- Energy
- 18.5 Wh
- Power draw
- 1.18 W
Quick answer
Battery runtime is capacity divided by average current, reduced by efficiency losses.
Hours = capacity (mAh) ÷ draw (mA) × efficiency
How to use the Battery Life Calculator
- 1Enter battery capacity in mAh.
- 2Enter average current draw in mA.
- 3Adjust usable capacity for real-world losses.
Frequently asked questions
Why is real runtime lower?
Cold, ageing cells and peak loads all cut usable capacity.
How do I convert to Wh?
Multiply mAh by voltage and divide by 1000.