Battery Life Calculator
Estimate how long a battery will last based on its capacity (mAh) and the circuit’s average current draw (mA). An optional efficiency factor accounts for real-world losses due to voltage regulation, battery chemistry, temperature, and discharge rate characteristics.
Estimated runtime
Runtime9 h 0 min
In hours9.00 h
Formulahours = capacity (mAh) ÷ load (mA) × efficiency
Formulas used
Battery Life (hours) = (Capacity in mAh × Efficiency) ÷ Load Current in mA
How to use this calculator
Step-by-Step Instructions
- Enter battery capacity Find this on the battery label (e.g., 18650 cells are typically 2000-3500mAh, 9V battery ~500mAh, AA ~2500mAh).
- Enter average load current Measure or calculate the average current draw of your entire circuit in milliamps (mA).
- Adjust efficiency Use 85-90% for Li-ion batteries with efficient regulators, 70-80% for alkaline batteries or inefficient circuits.
- Click Calculate Result shows estimated runtime in hours and days.
Worked Example
A 2000mAh Li-ion battery powering an ESP32 WiFi module drawing 150mA average:
(2000 × 0.85) ÷ 150 = 11.3 hours