Coin Cell Battery Life Calculator

Work out coin cell battery life instantly with clear inputs, formula shown and shareable results.

About Coin Cell Battery Life Calculator

A CR2032 has high internal resistance — often over 10 ohms as it ages — so a 15 mA radio pulse causes a large voltage sag that can brown-out the device long before the capacity is used. Life comes from average current, but feasibility comes from the pulse behaviour.

Formula

Coin cell life

life = usable capacity / average current; usable is typically 60-75% because of rising internal resistance

Worked example

With the default values below, Coin Cell Battery Life Calculator returns Battery life of 1.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Coin cell capacity: 225 mAh
Average current: 12 µA
Peak pulse current: 15 mA
Usable capacity: 70 %

Results

Battery life: 1.50 years
Usable capacity: 157.50 mAh
Peak current as multiple of rating: 66.67 x
Pulse load assessment: Add a 10-100 uF buffer capacitor to limit voltage sag

Step by step

1Values used
2Coin cell life
3Battery life= 1.50 years
4Usable capacity= 157.50 mAh
5Peak current as multiple of rating= 66.67 x
6Pulse load assessment= Add a 10-100 uF buffer capacitor to limit voltage sag

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why can a coin cell not supply a radio pulse?

Its internal resistance is tens of ohms when partly discharged. A 15 mA pulse then drops several hundred millivolts, tripping the brown-out detector.

What is the fix?

A bulk capacitor of 10-100 microfarads across the cell supplies the pulse and recharges slowly between transmissions.