Coin Cell Battery Life Calculator

Life of a duty-cycled sensor node on a coin cell, with two active phases and the cell’s own self-discharge: the average current, the life in days, months and years, and the share of the budget each consumer takes — plus the pulse-droop check that decides whether the radio burst browns the device out first.

Last updated 24 Sep 2026

Coin cell life

Duty cycle + self-discharge → years

Cell capacity (mAh)235 mAh for an Energizer CR2032 measured to 2.0 V through 15 kΩ; 225 mAh for a Panasonic CR2032. Both are LOW-drain ratings. Use the figures from your part’s datasheet; typical values vary widely between manufacturers.

Sleep current (µA)The whole board asleep: microcontroller, sensor, regulator quiescent current and any leakage.

Active current (mA)Awake, measuring and computing — but not transmitting.

Active time per cycle (ms)

Cycle period (s)How often the node wakes. 60 s means once a minute.

Radio burst current (mA)The transmit peak. Leave at 0 if the node has no radio.

Radio burst time per cycle (ms)

Self-discharge (%/year)About 1%/year for a lithium coin cell at 21 °C, and much more when warm.

Cell internal resistance (Ω)A fresh CR2032 is of the order of ten ohms; it rises steeply as the cell depletes and in the cold, reaching hundreds of ohms near the end.

Cell voltage on the plateau (V)About 2.9 V for most of a CR2032’s life, falling towards 2.0 V at the end.

Lowest voltage the device still works at (V)

The cell drawn with its own internal resistance in series, which is the whole point of the pulse warning: the controller's sleep and active currents are small enough that the drop across it does not matter, but the radio's burst is tens of milliamps and the drop is then tens or hundreds of millivolts to volts. The radio block turns amber as the loaded terminal voltage approaches the minimum the device needs and red once it is below it. The dots move at the AVERAGE current, which is what sets the life; the page's model knows nothing about the burst.

5.17yearsExample

a 235 mAh CR2032; 2 µA asleep, 5 mA for 20 ms and a 15 mA radio burst for 5 ms, once every 60 s, self-discharge 1%/year

Average current, and the ceiling self-discharge puts on it

I_av = I_active·d_active + I_tx·d_tx + I_sleep·(1 − d_active − d_tx) + I_self
d = on-time ÷ cycle period · I_self = capacity × (%/year) ÷ 100 ÷ 8,766 h
life = capacity ÷ I_av · burst droop = I_tx × R_cell

d: duty cycle of a phase: 20 ms every 60 s is 0.000333
I self: the cell emptying itself. 1%/year of 235 mAh is 268 nA — which is the floor no circuit design can get under
R cell: the cell’s internal resistance, of the order of ten ohms fresh and hundreds near the end of life
8,766: hours in a year, 365.25 × 24

Worked example

a 235 mAh CR2032; 2 µA asleep, 5 mA for 20 ms and a 15 mA radio burst for 5 ms, once every 60 s, self-discharge 1%/year
Duty cycles: 20 ms ÷ 60 s = 0.0333% active, 0.0083% transmitting, the rest asleep
Active 1.667 µA, burst 1.25 µA, sleep 1.999 µA, self-discharge 268.1 nA
I_av = 5.184 µA, so the life is 235 mAh ÷ 5.184 µA = 45,333 h = 1,889 days = 5.17 years
The budget splits 38.6% sleep, 32.2% active, 24.1% radio and 5.2% the cell leaking — so even a perfect zero-current sleep would only reach 8.42 years
The burst is the separate question: 15 mA through 15 Ω drops 0.225 V, taking the terminal to 2.675 V against a 2.0 V minimum. This cell can supply 60 mA before that margin is gone

What lowering the sleep current actually buys

The same node with everything else unchanged. Going from 20 µA to 2 µA is worth years; going from 0.5 µA to nothing at all is worth months, because by then the cell’s own leakage and the radio are what is left. Every figure computed by this page’s own arithmetic.
Sleep current	Average current	Life	Self-discharge share
20.0 µA	23.176 µA	1.16 years	1.2%
10.0 µA	13.181 µA	2.03 years	2.0%
5.0 µA	8.183 µA	3.28 years	3.3%
2.0 µA	5.184 µA	5.17 years	5.2%
1.0 µA	4.184 µA	6.41 years	6.4%
0.5 µA	3.685 µA	7.28 years	7.3%
0.0 µA	3.185 µA	8.42 years	8.4%

The burst, against the cell’s internal resistance

A CR2032’s resistance is not a constant: it starts in the low tens of ohms and climbs steeply as the cell depletes and in the cold. A radio burst that is comfortable on a fresh cell can reset the node on a half-empty one, with most of the rated capacity still unused — which is the failure the average-current model above cannot predict.
Cell resistance	Droop at 15 mA	Terminal voltage	Largest pulse to 2.0 V
5 Ω	0.075 V	2.825 V	180.0 mA
10 Ω	0.150 V	2.750 V	90.0 mA
15 Ω	0.225 V	2.675 V	60.0 mA
30 Ω	0.450 V	2.450 V	30.0 mA
60 Ω	0.900 V	2.000 V	15.0 mA
100 Ω	1.500 V	1.400 V	9.0 mA
200 Ω	3.000 V	-0.100 V	4.5 mA

Sleeping, waking, transmitting and leaking

A sensor node on a coin cell spends almost all of its life asleep. Its life is therefore set by four currents, not one: what it draws asleep, what it draws awake, what the radio draws while transmitting, and what the cell loses by itself. Each contributes its own current times its own share of the time, and the sum is the average current that empties the cell.

The arithmetic is simple and the insight is not. The example node wakes once a minute, measures for 20 ms at 5 mA and transmits for 5 ms at 15 mA. Those sound like the expensive parts, and they contribute 1.67 µA and 1.25 µA. Sleeping at 2 µA for 99.96% of the time contributes 2.00 µA — more than either. And the cell’s own 1% a year contributes 268 nA whatever the circuit does. Add them up and the average is 5.18 µA, which empties 235 mAh in about 5.2 years.

The ceiling. Suppose the sleep current went to zero — a perfect design, no leakage anywhere. The life goes to 8.4 years, not to infinity, because the other three consumers are still there and one of them is the cell emptying itself. That is the practical answer to “should I chase the last microamp?”: below a few microamps of sleep current the returns collapse, and the effort is better spent transmitting less often. The share rows on this page say exactly where you are on that curve.

The failure this model cannot predict. A CR2032 is a high-energy, low-power cell. Its internal resistance is of the order of ten ohms when fresh and rises steeply as it depletes — Murata’s technical note on these cells warns plainly that above about 10 mA the voltage drop becomes large, and that the device can stop working while the capacity is still there. Energizer’s own CR2032 sheet characterises the cell with a 400 Ω pulse drawing about 6.8 mA for two seconds, twelve times a day: that is the scale of pulse the manufacturer is prepared to describe. A radio burst of 15 or 30 mA through tens of ohms drops hundreds of millivolts, and through a depleted cell’s hundred-odd ohms it drops volts. The node browns out. Nothing in the average-current model above sees that coming, which is why this page computes the droop and the largest pulse the cell can supply as separate answers, and why a reservoir capacitor across the cell — sized to carry the burst at a droop you choose — is standard practice. For that capacitor’s own arithmetic, the capacitor energy and hold-up calculator does the hold-up sums properly, ESR included.

What is left out. Temperature, which changes both the capacity and the resistance, and which makes self-discharge much worse above about 40 °C. The fact that the rated capacity is measured at a low continuous drain and is not all available to a pulsed load. Regulator and boost-converter losses if the node has one. And the cell voltage falling through the life, which raises the current a regulated load draws. For a general battery and a continuous or single-phase duty-cycled load, the battery life calculator covers depth of discharge and Peukert’s law as well.

Frequently asked questions

How long will a CR2032 last in a sensor?

Work out the average current. A node sleeping at 2 µA, waking for 20 ms at 5 mA and transmitting for 5 ms at 15 mA once a minute averages 5.18 µA including self-discharge, so a 235 mAh cell lasts about 5.2 years.

Why does reducing sleep current stop helping?

Because the cell empties itself too. At 1%/year a 235 mAh coin cell leaks 268 nA whatever your circuit does, and the active and transmit phases add their own averages. Once sleep is a small share of the total, halving it changes the life very little — this page shows the share so you can see where you are.

What is the self-discharge of a coin cell?

About 1% a year at room temperature for a lithium manganese dioxide cell such as a CR2032, which is where the familiar ten-year shelf life comes from. It rises steeply with temperature.

Why does my node reset when the radio transmits?

Because the cell has real internal resistance and the burst is tens of milliamps. 15 mA through 15 Ω is 225 mV; through a depleted cell’s 100 Ω it is 1.5 V, which takes a 2.9 V cell below almost any brown-out threshold. Add a reservoir capacitor across the cell to carry the burst.

How big should the reservoir capacitor be?

Enough that the burst’s charge does not move its voltage more than you can afford: C = I × t ÷ ΔV. A 15 mA burst lasting 5 ms within 100 mV needs 750 µF. Check its ESR too, because a high-ESR capacitor reintroduces the problem.

Does this work for AA lithium or a rechargeable cell?

The average-current arithmetic works for any cell. Change the capacity and the self-discharge figure, and change the internal resistance — an AA lithium cell is well under an ohm, so the pulse warning rarely applies to it.

Related calculators

References

Energizer. CR2032 product datasheet: 3.0 V nominal, rated capacity 235 mAh to 2.0 V on a 15 kΩ continuous load at 21 °C, approximately 1%/year self-discharge at 21 °C, 3.0 g, −30 to 60 °C, and a pulse characterisation of 2 seconds twelve times a day through 400 Ω, giving about 6.8 mA at 2.7 V.
Murata. Technical Note of Coin Manganese Dioxide Lithium Battery (TCN-CR-001): “when high drain (more than 10 mA) is discharged from battery, the voltage drop becomes large”, and “even if the battery capacity is sufficient, the voltage drop may cause the minimum drive voltage of the device to drop and the device may become inoperable”. Murata’s high-drain type reduces internal resistance by 30% against the standard product for exactly this reason.
Panasonic. CR2032 datasheet: 3 V nominal, 225 mAh nominal capacity at a 0.2 mA standard drain, −30 to +85 °C, approximately 2.8 g.
Reddy TB (ed.). Linden’s Handbook of Batteries, 4th ed. McGraw-Hill, 2011. Lithium/manganese dioxide primary cells: internal resistance, pulse capability and the effect of depth of discharge on impedance.