Bangle.js2 E.getBattery() never reaches 100 %

Ahh, thanks! That's interesting - it looks like the 'full charge' voltage condition isn't quite right.

If you run analogRead(D3) you can see what the actual value returned is (this is 0..1, so it's more like ~1v). I'll try with a unit here, but right now I see 0.3181 with it on charge (although it wasn't quite a full charge before).

I think there's a distinct possibility I rounded 0.3181(ish) to 0.32, without really considering that it wouldn't quite hit 100%.

is there a better way to detect the 'end-of-charge' condition ?

Not really. You may be able to detect when the 'charging' status changes (I can't recall if that works on Bangle.js 2 or not) but you can't tell if that's because it was full or it was unplugged.

I think the best thing for me to do is to update the firmware, but obviously that's not ideal for the devices you have in the field right now. You could do this in JS in the mean time:

if (process.version=="2v10.89") {
  E.getBattery = (oldGetBattery=>()=>Math.min(oldGetBattery()*105,100))(E.getBattery);
}