Device Battery Life
Estimate battery life for phones, tablets, and laptops from capacity, screen brightness, and usage.
Calculate charge cycles and expected battery lifespan.
Battery life is calculated in two steps. First, convert the battery capacity from milliamp-hours (mAh) to watt-hours (Wh). Then divide by the average power draw.
Watt-hours (Wh) = (mAh × Voltage) / 1000
Battery Life (hours) = Wh / Average Power Draw (W)
What the variables mean:
- mAh (milliamp-hours): The battery capacity listed on your device specs. Higher means more stored energy.
- Voltage (V): The battery operating voltage. Most smartphones and tablets use 3.7V lithium batteries. Laptops typically use 7.4V or 11.1V.
- Power draw (W): How much power your device consumes on average during use.
Typical battery capacities and power draws:
| Device | Battery (mAh) | Voltage | Approx Wh | Typical Draw |
|---|---|---|---|---|
| Smartphone | 4,000-5,500 | 3.7V | 15-20 Wh | 2-4 W |
| Tablet | 7,000-10,000 | 3.7V | 26-37 Wh | 3-6 W |
| Laptop | 4,000-6,000 | 11.1V | 45-67 Wh | 10-30 W |
Practical example: A phone with a 5,000 mAh battery at 3.7V has 18.5 Wh of energy. At an average draw of 3W (light browsing), it lasts about 6 hours and 10 minutes.
Tips: Screen brightness is the single biggest factor in power draw. Reducing brightness from 100% to 50% can extend battery life by 30% or more. WiFi uses less power than cellular data. Background apps and GPS also increase drain significantly.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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