Battery Life Calculator
Runtime from capacity and current draw.
Enter your values
ⓘ Live results
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.
Worked example
Using the values the calculator loads with:
Inputs
- Battery capacity5000 mAh
- Average draw320 mA
- Voltage3.7 V
- Usable capacity85 %
Results
- Runtime13.3 hours
- Runtime in days0.55
- Energy18.5 Wh
- Power draw1.18 W
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.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.