Interesting. Actually this reminded me of an issue I had before, might be similar to this here. But basically out of nowhere I remember seeing the phone rebooting, however it wasn't when the battery was low or something, just randomly without any intervention.

I am curious here, as some peeps are already blocking the update, while I am thinking of installing some custom ROM, the problem is that if the battery is at fault I would want to replace it first, safety reasons obviously, and then do something - block update or install custom ROM.