April 25, 2014 AT 11:29 am

How Much Energy Can You Get From A Coin Cell?

coincell

Embedded legend Jack Ganssle tackles the question of how much juice you can pull from a coin cell. He writes:

About a year ago I wrote of my on-going experiments to determine how coin cells behave. This was motivated by what I consider outrageous claims made by a number of MCU vendors that their processors can run for several decades from a single CR2032 cell. Some vendors take their MCU’s sleep currents and divide those into the battery’s 225 mAh capacity to get these figures. Of course, no battery vendor I’ve found specifies a shelf life longer than a decade (at least one was unable to define “shelf life”) so it’s folly, or worse, to suggest to engineers that their systems can run for far longer than the components they’re based on last.

Conservative design means recognizing that ten years is the max life one can expect from a coin cell. In practice, even that will not be achievable.

There’s also a war raging about which MCUs have the lowest sleep currents. Sleep current is, to a first approximation, irrelevant, as I showed last year.

But how do coin cells really behave in these low-power applications? I’ve been discharging CR2032s with complex loads applied for short periods of time and have acquired millions of data points.


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