Happened to me recently. Deleting Clockology and Clockology faces solved my problem. I think that is because it is constantly transferring info and watchos 10 sped it up. You can also try deleting any app like this

I turned off my watch when it was at 33% battery life. When I turned it back on and charged it the battery drained rapidly after that and then it was shutting off when it got to 33%. My watch somehow got tricked into thinking 33% was 0%. This was a couple years ago so I can’t exactly remember how I fixed it but I found the solution via Google and it’s been perfect ever since.