Battery Life Calculator

Battery life = Battery capacity (mAh) ÷ Device consumption (mA). For example, a 3000mAh battery powering a device that draws 500mA will last 3000÷500 = 6 hours. This assumes 100% efficiency—real-world runtime is typically 80-90% of calculated values due to voltage drop, heat loss, and the battery not delivering its full rated capacity.

mAh (milliamp-hours) measures battery capacity—how much charge a battery can store. A 2000mAh battery can theoretically deliver 2000mA for 1 hour, 1000mA for 2 hours, or 200mA for 10 hours. Higher mAh means longer runtime. However, mAh doesn't account for voltage, so comparing batteries requires the same voltage or converting to Wh (watt-hours) for accurate comparison.

Wh = mAh × Voltage ÷ 1000. For example, a 3000mAh battery at 3.7V = 3000 × 3.7 ÷ 1000 = 11.1Wh. Watt-hours measure total energy storage regardless of voltage, making it better for comparing different battery types. A 5000mAh power bank at 3.7V (18.5Wh) stores less energy than a laptop battery at 7.4V with 3000mAh (22.2Wh).

Several factors reduce real-world battery life: (1) Efficiency losses in voltage conversion (typically 80-95%); (2) Batteries don't deliver 100% of rated capacity, especially when discharged quickly; (3) Temperature affects capacity—cold reduces it significantly; (4) Device consumption varies with usage, not constant; (5) Battery age and health matter—capacity degrades over charge cycles. Expect 70-90% of calculated runtime.

Calculate: Capacity needed = Device consumption (mA) × Runtime (hours) ÷ Efficiency (0.8-0.9). For a project drawing 200mA that needs 24 hours runtime: 200 × 24 ÷ 0.85 = 5647mAh, so choose a 6000mAh battery. Always add 15-20% margin for safety. For critical applications, consider temperature, battery aging, and worst-case power consumption in your calculations.