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> That is likely even lower than the effective self discharge rate of a lithium coin cell battery.

That's what I've found too. Based on my measurements and calculations, Photon uses 5µA (MSP430 + motion sensor) while sleeping, while the battery's self-discharge is more like 80µA.

That's probably a good argument for using a more powerful chip though, if the battery self-discharge is that high, hah.

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Maybe tiny solar panel + capacitor, like 1980/90s calculators had, then it could run "forever" - digital Millennium Camera.

This is a cool idea!

Or a different battery chemistry with a lower self discharge rate. No need to be rechargable in most of the use cases, I'd imagine.

This sounds like a job for a lithium thionyl chloride battery.

The guys with the purple LiSoCl2 batteries make ones with up to 40 years of usable life

Panasonic BR2032 has 30µA discharge rate https://www.digikey.com/en/products/detail/panasonic-bsg/BR-...

If that's the self discharge rate then the battery would be fully discharged after less than a year on the shelf (given its 190mAh capacity). Coin cells typically have a much longer shelf life than that. I wonder what that figure is, exactly.

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