How long a battery lasts depends on its capacity and its load. This battery runtime calculator takes the active and sleep current of a device that wakes, or one average current. The result includes a derating margin and self-discharge, with a chart of the charge remaining over time.
Batteries in series add voltage, not mAh: 2 × AA is still one AA of capacity.
Your margin for temperature, pulses, aging and cut-off voltage.
Percent of the remaining charge lost per month at rest.
Include regulator quiescent current and leakage.
Time from one wake-up to the next: 60 for once a minute, 3600 for hourly.
Estimated battery life
2.84 years
CR2032 capacity is rated at a steady 0.2 mA. Pulses above that reduce what you get, so keep a real derating margin.
What the wake interval does to battery life
| Wake every | Average current | Battery life |
|---|---|---|
| 1 s | 52 µA | 144 days |
| 10 s | 7 µA | 2.84 years |
| 1 min | 2.83 µA | 6.73 years |
| 10 min | 2.08 µA | 8.93 years |
| 1 h | 2.01 µA | 9.21 years |
| 1 day | 2 µA | 9.27 years |
Battery life in hours = usable capacity in mAh ÷ average current in mA. A CR2032 derated to 180 mAh, feeding a device that averages 7 µA, lasts about 2.84 years once self-discharge is included. For a device that sleeps, average the current over one full wake period first.
Charge is conserved, so what matters is the average current over a whole wake period. Short bursts count in proportion to how long they last.
The usable charge is the rated capacity less your margin. With no self-discharge the life is simply:
Self-discharge is modeled as a loss proportional to the charge still in the cell. Solving dQ/dt = −Iavg − kQ gives the charge remaining and the time to empty:
10 mA for 5 ms and 2 µA for the rest of a 10 s period averages 7 µA. The active bursts use 71.4 % of that charge and sleep the rest, so both are worth reducing. A 225 mAh cell derated 20 % leaves 180 mAh. Load only that is 2.93 years; with 0.18 % per month of self-discharge the result is 2.84 years.
30 mA for 2 s every 5 min with 15 µA of sleep current averages 215 µA. Two cells in series still hold 2500 mAh, so derating 15 % gives 2125 mAh and a life of 405 days.
60 mA for 30 s every 10 min and 100 µA asleep averages 3.09 mA. From 2400 mAh usable, the battery lasts 32 days. Active time is 5 % of the period but dominates the charge used, so a shorter GPS fix is the biggest lever.
Using the same margins as the presets. A dash means the current is above what that cell is rated or characterized for, so its rated capacity no longer applies. Results past ten years are not meaningful: shelf life takes over.
| Battery | 5 µA | 20 µA | 100 µA | 1 mA | 10 mA | 100 mA |
|---|---|---|---|---|---|---|
| CR2032 (225 mAh) | 3.93 years | 371 days | 74.8 days | — | — | — |
| 2 × AA alkaline (2500 mAh) | Over 10 years | Over 10 years | 2.34 years | 88.2 days | 8.85 days | 21.2 hours |
| 18650 Li-ion (3000 mAh) | Over 10 years | 6.03 years | 2.1 years | 96.8 days | 9.97 days | 24 hours |
A 225 mAh CR2032 derated 20 %, with 10 mA for 5 ms per wake and 2 µA of sleep current. Past a point, waking less often gains little because sleep current and self-discharge take over.
| Wake every | Average current | Battery life |
|---|---|---|
| 1 s | 52 µA | 144 days |
| 10 s | 7 µA | 2.84 years |
| 1 min | 2.83 µA | 6.73 years |
| 10 min | 2.08 µA | 8.93 years |
| 1 h | 2.01 µA | 9.21 years |
| 1 day | 2 µA | 9.27 years |
Capacity is always quoted at a specific load and end voltage. Check your own cell’s datasheet.
| Battery | Rated capacity | Rated at | Self-discharge used |
|---|---|---|---|
| CR2032 (Panasonic) | 225 mAh | 0.2 mA continuous drain | 0.18 %/month (10 % in 5 years) |
| AA alkaline (Energizer) | 2500 mAh | 100 mA to 0.8 V | 0.25 %/month (about 3 %/year) |
| 18650 Li-ion (Samsung 30Q) | 3000 mAh | 0.2C to 2.5 V | 2 %/month |
Divide the usable capacity in mAh by the average current in mA to get hours. For a device that sleeps and wakes, the average current is (active current × active time + sleep current × sleep time) ÷ the total period.
It depends almost entirely on the average current. A node drawing 10 mA for 5 ms every 10 s and sleeping at 2 µA averages 7 µA, which gives about 2.84 years with a 20 % derating. Load the CR2032 preset to try your own numbers.
Divide the capacity in mAh by the current in mA: ideally, 1000 mAh delivers 1 A for one hour or 1 mA for 1000 hours. A plain mAh to hours calculator stops there, while this one also subtracts a derating margin and self-discharge.
Yes. Choose the Average current mode and enter the steady draw, as the steady 18650 preset does. For a constant load the result is usable mAh divided by mA, with self-discharge still counted.
There is no universal figure, so treat it as your margin for cold, high pulses, aging and a device cut-off voltage above the rated end voltage. The presets use 15 to 20 %. Use more for CR2032 cells that see radio pulses: TI measured some vendors at about 50 % of rated capacity with 15 mA and 30 mA peaks.
It matters when the load is tiny. In the CR2032 example it costs 3.04 % of the runtime; at higher currents it fades to nothing. Published figures are about 3 % per year for alkaline cells, about 10 % in 5 years for primary lithium, and 1 to 2 % per month for Li-ion.
No. In series the voltage doubles and the capacity stays at one cell’s mAh. Two cells in parallel double the mAh instead. With a switching regulator, the extra energy of a series pair shows up as a lower input current; with a linear regulator it does not.
The most common causes are current peaks far above the 0.2 mA the CR2032 is rated at, cold temperatures, and sleep current that is higher than the datasheet of the microcontroller alone (regulators, pull-ups and sensors all add to it). Measure the real sleep current and add a bulk capacitor across the cell for radio bursts.
Measure the current over one full wake cycle and take the mean, or add up each state as current × time and divide by the period. If you have more than two states, sum them all first and use the Average current mode.
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