Battery Life Calculator
Accurately estimate battery runtime, energy consumption, and effective capacity for your electronic devices.
Last reviewed: June 2026Common Battery Reference
Runtime estimates use your current draw and efficiency settings above.
| Battery | Capacity | Voltage | Runtime at your load |
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How the Battery Life Calculator Works
This calculator estimates runtime from the electrical load you enter, not from a phone-style percent drain estimate. The basic model is: effective capacity = battery capacity x efficiency, then runtime = effective capacity / average current draw. With the default 3000 mAh battery, 70% efficiency, and 100 mA average current, the effective capacity is 2100 mAh and the estimated runtime is 21.0 hours.
The energy result is separate from runtime. It uses the nameplate capacity and nominal voltage: watt-hours = mAh / 1000 x volts. A 3000 mAh cell at 3.7 V is about 11.10 Wh before allowing for conversion losses. That makes Wh the better comparison when two packs have different voltages, while mAh is useful only when the voltage is similar.
Duty-Cycle Mode
Duty-cycle mode is for projects that alternate between active and low-power states, such as sensors, radios, embedded boards, and small IoT devices. The calculator uses average current = active current x active time + sleep current x sleep time. With the default duty-cycle values, 500 mA for 10% of the time and 5 mA for 90% of the time averages to 54.5 mA. The same 3000 mAh battery at 70% efficiency then lasts about 38.5 hours instead of 21.0 hours.
What the Efficiency Input Represents
The efficiency field is a practical derating factor. It can represent regulator losses, boost-converter losses, voltage cutoff behavior, cold weather, cell age, and usable-capacity limits under load. A simple LED circuit powered directly from a battery may justify a higher value. A microcontroller with a boost converter, radio bursts, and a conservative cutoff voltage may need a lower value.
Common Mistakes
Do not divide mAh by a daily battery percentage. Percent drain is a result of a device's internal power management, not an electrical load. Do not compare a 5000 mAh USB power bank directly with a 5000 mAh 12 V pack without converting to Wh. Also check units: 1 A is 1000 mA, so entering amps as milliamps can be off by a factor of 1000.
Battery datasheets usually rate capacity at a specific discharge rate, temperature, and cutoff voltage. High current draw, cold cells, old batteries, and low-quality cells can all reduce usable capacity. For product design, measure current with the real hardware in active, idle, and sleep states, then enter those measured values rather than relying on marketing battery capacity.
Using Daily Use and Charge Cycles
The optional daily-use field estimates charge cycles per year. If a device has 21 hours of runtime and you use it 3 hours per day, the calculator estimates about 52 charge cycles per year. That number helps compare operating patterns, but it does not model partial-cycle battery aging chemistry in detail.