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Battery Runtime Calculator

Created by Gregor A. • Published on October 11, 2026

Battery Runtime Calculator: How long does my battery last? Works for power banks, e-bikes, ESP32 projects and tool batteries. cellVoltage = 3.6 V

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How long does my battery last?
Works for power banks, e-bikes, ESP32 projects and tool batteries.
Battery
cellVoltage = 3.6 V
cellCapacity = 3000 mAh
cellsInSeries = 3
cellsInParallel = 2
usableDepth = 90 % Energy
packVoltage = cellVoltage * cellsInSeries
packCapacity = cellCapacity * cellsInParallel
energy = packVoltage * packCapacity * usableDepth to Wh Load
loadPower = 18 W
runtime = energy / loadPower to hours Or work out what load gives a wanted runtime
wantedRuntime = 8 hours
maxLoad = energy / wantedRuntime to W
maxCurrent = maxLoad / packVoltage to A