Battery Life Calculator
Estimate battery runtime in hours from capacity (mAh or Wh) and device current draw. Compare battery options for laptops
Battery Specifications
Device Power Consumption
Environmental Factors
Battery Life
Battery Life
1.3 days
10.1 hours total
Power Consumption
500.0 mW
Average draw
Daily Energy
4.0 Wh
Energy per day
Usable Capacity
5.0 Wh
68.0% of rated
Efficiency
100.0%
Temperature effect
Capacity Analysis
Rated Capacity:7.4 Wh
Temperature Effect:100.0%
Age Effect:100.0%
Reserve Capacity:20%
Usable Capacity:5.0 Wh
Power Saving Tips
• Reduce screen brightness-75.0mW
• Enable power saving mode-125.0mW
• Disable unnecessary features-100.0mW
• Optimize usage patterns-50.0mW
How it works
Battery life estimates how long a device runs on a charge by dividing the battery's capacity by the current the device draws. Capacity is in milliamp-hours (mAh) and draw in milliamps (mA), so the result is in hours — discounted a bit for real-world inefficiency.
Runtime
Hours ≈ (capacity mAh ÷ draw mA) × efficiency
- capacity
- battery rating in mAh
- draw
- device current draw in mA
- efficiency
- ~0.7–0.85 for real losses
Worked example
- Battery = 3,000 mAh
- Device draws 250 mA, efficiency 0.8
- 3,000 ÷ 250 = 12 hours ideal
- × 0.8
≈ 9.6 hours of real-world runtime.
Good to know
- Apply an efficiency factor (often 0.7–0.85) — heat, voltage conversion, and aging all cut into the ideal figure.
- Higher current draw (brighter screen, more processing) shortens runtime proportionally.
- Batteries lose capacity as they age, so an old pack won't hit its rated mAh.