Electronics · Free Calculator
Battery Life Calculator for Electronic Devices
Estimate the run time of a battery powered sensor or device that wakes up, works and goes back to sleep.
mAh capacitySleep currentDuty cycleHours and days
mAh
mA
% of time
µA
%
Battery life3,786 h
In days157.8 days
In years0.432 years
Average current0.449 mA
Share of sleep current10.9 %
How this result was calculated
- Iavg = 20 mA × 0.02 + 0.05 mA × 0.98 = 0.449 mA
- Life = 2,000 mAh × 0.85 ÷ 0.449 mA = 3,786 h
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Battery Life Formula
Iavg = Iactive × D + Isleep × (1 − D)
Life (h) = Capacity (mAh) × usable fraction ÷ Iavg (mA)
Life (h) = Capacity (mAh) × usable fraction ÷ Iavg (mA)
The usable fraction allows for cut off voltage, temperature and ageing; 70 to 85 % is a sensible planning figure.
Worked example
A 2000 mAh cell powers a node that draws 20 mA for 2 % of the time and 50 µA asleep: Iavg = 0.449 mA, so life = 1700 ÷ 0.449 = 3786 h (158 days).
Key insight: in low power designs the sleep current often dominates; cutting 50 µA to 5 µA here would extend life by about 10 %, while halving the active time gives far more.
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Frequently Asked Questions
How do I calculate battery life?
Divide usable capacity in mAh by the average current in mA to get hours.
Why not use the full rated mAh?
Rated capacity is measured at low current and room temperature; real loads, cold and ageing reduce it.
How long will a 2000 mAh battery last at 100 mA?
About 17 hours using 85 % of capacity.
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