Just sharing my similar experience. Reboots 4-5 times in succession on a run, low battery signal in between, stabilizes to 10% battery (from 95%). Was on with Apple Support (chat, to senior technician), was offered a replacement that was somehow denied at the store. The store send the watch to the repair center, who reported that everything was working just as it should! So a lot of time wasted, including going into a mall during COVID lockdowns, all for nothing at this point.