Battery Life Calculator — with sleep-mode duty cycling
Runtime from capacity and load — including a duty-cycled sleep profile for battery-powered IoT nodes that spend most of their life asleep.
Example: A 2 Ah battery at 50 mA average draw lasts about 32 hours.
Formula
runtime = capacity × derating / average currentWorked example
A 2 Ah battery at 50 mA average draw lasts about 32 hours.
usable = capacity × derating
usable = 2 Ah × 0.8
usable = 1.6 Ah
runtime = usable / I_avg
runtime = 1.6 Ah / 50 mA
runtime = 32 hours (32 hours)
Frequently asked questions
How long will a 2000 mAh battery last at 100 mA?
About 20 hours in theory, and closer to 16 in practice once you allow for the fact that nameplate capacity is measured under ideal conditions. Divide capacity by current for the ideal figure, then apply a derating of 70–90%.
Why does my battery-powered sensor die so much sooner than calculated?
Almost always because the calculation used the active current for all of the time. A sensor that wakes for 100 ms every 10 seconds is asleep 99% of the time, so its sleep current dominates. Use the duty-cycle fields above — the answer often changes by 10× or more.
What sleep current should I expect?
A well-configured microcontroller in deep sleep is typically 1–10 µA. If you measure hundreds of µA, something is still powered: a linear regulator's quiescent draw, a pull-up through a pressed button, an LED, or a peripheral that was never put to sleep.
Why can't I use the full rated capacity?
Datasheet capacity comes from a gentle constant-current discharge at room temperature down to a low cut-off voltage. Real circuits stop working when the supply falls below their minimum, higher currents deliver less total charge, and cold weather takes more still. 70–90% of nameplate is realistic.
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