You are reading a single comment by @Gordon and its replies.
Click here to read the full conversation.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
Ok, great.
Honestly, I'd just use a big non-rechargeable lithium battery. If you use an AA format non-rechargeable lithium you're looking at ~2500mAh and often a 10 year life: https://uk.farnell.com/c/batteries-chargers/batteries-non-rechargeable?battery-voltage=3.6v
Then I'd just attach it to the 3.3v rail of the MDBT42Q breakout board with a diode. That way if the 3.3v rail ever drops (because the voltage source powering it fails) then the battery will take up the slack, but it won't be powering it normally.