How to use the battery life calculator
- Enter the battery capacity and active current.
- For devices that sleep, enter the active duty and sleep current.
- Adjust the derating for your conditions and read the runtime in hours and days.
Battery life chart
Battery life (hours) = usable capacity (mAh) ÷ average current (mA). The table uses 85% of the rated capacity because cold, high current, cut-off voltage and ageing all reduce it; h = hours, d = days.
| Capacity | 1 mA | 10 mA | 50 mA | 100 mA | 500 mA |
|---|---|---|---|---|---|
| 220 mAh | 7.8 d | 18.7 h | 3.7 h | 1.9 h | 0.4 h |
| 1,000 mAh | 35.4 d | 3.5 d | 17 h | 8.5 h | 1.7 h |
| 2,500 mAh | 88.5 d | 8.9 d | 42.5 h | 21.2 h | 4.2 h |
| 3,400 mAh | 120.4 d | 12 d | 2.4 d | 28.9 h | 5.8 h |
| 5,000 mAh | 177.1 d | 17.7 d | 3.5 d | 42.5 h | 8.5 h |
| 10,000 mAh | 354.2 d | 35.4 d | 7.1 d | 3.5 d | 17 h |
| Battery | Nominal voltage | Typical capacity |
|---|---|---|
| CR2032 coin cell | 3 V | 220–240 mAh |
| AAA alkaline | 1.5 V | 1,000–1,200 mAh |
| AA alkaline | 1.5 V | 2,500–3,000 mAh |
| AA NiMH | 1.2 V | 1,900–2,500 mAh |
| 9 V alkaline | 9 V | 500–600 mAh |
| 18650 Li-ion | 3.6–3.7 V | 2,500–3,500 mAh |
| 21700 Li-ion | 3.6–3.7 V | 4,000–5,000 mAh |
| Phone Li-po pack | 3.85 V | 3,000–5,000 mAh |
| 12 V 7 Ah lead-acid | 12 V | 7,000 mAh |
Capacity varies widely by brand and discharge rate; use the datasheet.
Frequently asked questions
How is battery life calculated?
Runtime (hours) = usable capacity (mAh) ÷ average current (mA). For devices that sleep, average current = active current × duty + sleep current × (1 − duty).
Why is real runtime shorter?
Rated capacity is measured at low current and room temperature. High current, cold, a high cut-off voltage, ageing and self-discharge all reduce it, so the calculator derates by 15% by default.
How do mAh and Wh convert?
Wh = mAh × voltage ÷ 1000, so a 3.7 V 3000 mAh cell holds about 11.1 Wh. Compare batteries of different voltages in Wh.
Are my inputs uploaded?
No. Everything is calculated locally in your browser and nothing is stored; a share link only carries the values you entered.
Results are for design estimates and part selection; for production and safety-related circuits follow component datasheets, applicable standards and measurements.