Bangle2 died on low power - did not shut itself down?

That's an odd one - what did the corrupted screen actually look like? Is it possible the watch display just got really cold in this weather?

Usually there's a little more power left after it reaches 0% (and the watch will just work normally reading 0% until it turns off) but the hardware should automatically shut off when the battery reaches ~3v, which is well within spec for the components.

To get low enough for real problems, I'd expect from that Gadgetbridge graph that the charge display would have stayed on 0% for some time