Battery Life Calculator
Capacity divided by draw, then trimmed by reality. Find out whether your sensor runs for a weekend or a winter.
mAh
mA
%
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Why the efficiency factor
Capacity ÷ draw gives the textbook answer: 2000 mAh at 80 mA is 25 hours. Real batteries deliver less. Ratings are measured at gentle currents and room temperature, converters waste a slice, and cells age. Derating to 85% is honest for fresh alkalines at modest draw; drop toward 70% for cold weather, high current, or cells of mysterious provenance.
Average draw is the hard part
A microcontroller that sleeps at 10 µA and wakes to 80 mA for two seconds each minute averages under 3 mA. Weight the on and off currents by their share of the cycle and use that number here: it's the difference between a battery estimate in days and one in months.