Motivated by what he considers outrageous claims made by a number of MCU vendors that their processors can run for several decades from a single CR2032 cell, Jack Ganssle compares coin cell batteries to see if the claims are legit.
About a year ago I wrote of my ongoing 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 10 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.
My CR2032 experiment. A small ARM controller applies various loads to batteries being discharged and logs the results.
(Source: Embedded.com/ Jack Ganssle)
The following results are for 42 batteries from Duracell, Energizer, and Panasonic. For each vendor I ran two groups of cells, each group purchased months apart from distributors located in distant states, in hopes that these represent different batches. (The devices are not marked with any sort of serial or batch numbers.)
The story continues on EE Times' sister site, Embedded.com.