Bangle.js2 keeps crashing?

When it does crash, the only way to get it started again is to attach the power lead that seems to get the screen back on, and then log presses cause a restart.

Normally, this would be exactly what happens for a flat battery.

Have you tried just leaving the Bangle on charge over night? I know you say it reports the battery is fully charged, but on some Bangles the battery charge isn't calibrated properly. There's code in the firmware to take an updated calibration value, so if it's the case on yours it's easy to fix.

If you're not leaving it charging because the battery is saying it's full then it's most likely your issue - of course I guess it is possible it really is a battery issue in which case we'll sort out a replacement.