I charge mine overnight. Sometimes no problem, sometimes it charges to 100%, then drains to 56% then stops charging altogether. And when at 56% sometimes I can take it off the charger, put it back and charging starts, sometimes it doesn't. I have the cable that came with the watch, a Native Union cable, the cable from my last watch (Series 8). I've tried connecting each of those to various chargers, including direct to my PC (that worked once but not since).
Yesterday I had to re-boot my watch to get it to charge, today just remove from the charger and put it back. Tonight I will charge my watch to 100% and not leave it on charge overnight and see if it drains without being on the charger.
The watch was fine when I first bought it (4th Feb 25) and about a week later failed to charge but then was fine until after the last OS update.
Glad it is not just me. I don't really want to have to buy yet another charger (wall plug) to add to my collection of chargers (I mainly use an Anker charger with two old style usb connectors and two USB c which has been charging my iPhone 16 Pro Max - and my previous 14 Pro Max - an iPad Mini and an iPad without problem)