The calculator below estimates how long a battery will last for a given load. It works by simulating the battery month-by-month: each month it first removes the self-discharge (a percentage of the remaining charge — see self-discharge), then subtracts the charge consumed by the load and the protection circuit module (PCM). The battery is considered flat once the usable capacity has been consumed.
The load is modelled as a duty-cycled device with an active current and a sleep current — set the duty cycle to 0% if your load just draws a single constant current (enter it as the sleep current). The temperature input scales the self-discharge rate against a 25 °C reference, doubling it for every 10 °C above and halving it for every 10 °C below (reff=r25°C⋅2(T−25)/10); the load and PCM currents are assumed to be temperature-independent. The end-of-life capacity lets you model an aged cell.
Estimate how long a battery will last, simulated month-by-month. Each month self-discharge removes a percentage of the remaining charge, then the load and protection-circuit (PCM) currents draw a fixed amount. The battery is "dead" once the usable capacity is spent.
Capacity
mAh
Rated cell capacity.
Iactive
A
Current the load draws while active/awake. Only used when the duty cycle is above 0%.
Duty
%
Percentage of time the load is active. 0% means the load is always in its sleep state.
Isleep
A
Current the load draws while idle/asleep (the average load equals this when duty = 0%).
IPCM
A
Quiescent current of the battery's protection circuit module. Always drawn, on top of the load.
Self-dis.
%/mo
Self-discharge per month, as a percentage of remaining charge, at 25 °C.
Usable
%
Fraction of capacity actually extractable before the cut-off voltage is hit. Li-ion is rarely run down to 0%.
Temp.
°C
Ambient temperature. Self-discharge roughly doubles for every +10 °C above 25 °C.
EOL cap.
%
Capacity remaining relative to rated, to model an aged cell (e.g. 80% near end-of-life). Use 100% for a fresh cell.
NinjaCalc
