Battery life calculator
Current-draw states
Add up to three states with a current draw and the percentage of time spent in each. Duty cycles should add up to 100%.
Result
Average current-
Estimated battery life-
Battery Life Estimator
Estimate battery runtime from capacity and up to three current-draw states with duty cycles, such as active, sleep, and radio burst current for a low-power sensor node.
Why average current, not peak current, determines battery life
A device that draws 10 mA for a brief active burst and 2 µA the rest of the time behaves, from the battery's perspective, like a device drawing whatever the time-weighted average of those currents works out to. That average, not the peak, is what determines how many hours the stored charge will last.
Why duty cycle dominates low-power design
Cutting active current in half only helps as much as the fraction of time spent active. If a sensor node spends 99.9% of its life asleep, halving sleep current usually saves far more total energy than halving active current, which is why low-power firmware work focuses so heavily on sleep-mode current and wake frequency.
What this estimate does not account for
Real batteries lose usable capacity to self-discharge, temperature, and a voltage cutoff before they are fully depleted, and coin cells in particular sag under brief current pulses. The usable capacity field lets you apply a derating factor from your battery's datasheet instead of assuming the full rated mAh is available.
FAQ
Why does my calculated battery life not match what I see in real devices?
This estimate assumes a linear, ideal battery. Real cells have internal resistance that causes voltage sag under load, self-discharge over time, and reduced usable capacity at low temperatures, all of which shorten real-world life relative to the ideal calculation.
How many current-draw states should I model?
Two states, active and sleep, cover most simple designs. A third state is useful for devices with a distinct high-current burst, such as a radio transmit pulse, that is short but draws far more current than the active state alone.
What should I set the usable capacity percentage to?
100% treats the full rated capacity as available. Many real designs use 70 to 90% to account for a battery's voltage dropping below the device's minimum operating voltage before the cell is chemically empty, especially for coin cells under pulsed loads.
Does the order of duty cycle percentages matter?
No, only the current and duty cycle pairing for each state matters. The calculator computes the same weighted average current regardless of which row a given state is entered in.
My duty cycles do not add up to 100%. What happens?
The calculator still computes a result using exactly the values entered, but shows a warning so you can fix the inputs. A common cause is forgetting a third state, or leaving one field blank when it should be filled in.
Does cells in parallel work the same as cells in series?
No. Cells wired in parallel add capacity, which is what the cells-in-parallel field multiplies. Cells wired in series add voltage instead and leave the pack's total mAh the same as a single cell, so a series count would not change this calculator's result at all.