My Apple SE (96% battery health) was on WatchOS 9.6 and I was afraid of updating
I switched from Iphone 12 to Iphone 15 Plus, unpair/pair the watch and I don’t know why I was forced to update to WatchOs 10.
Then I decided to leave it on charger for 2-3 hours on charger then shut it off.
I turn it on to try Watch OS 10 : good battery life, animations are smooth !
I don’t know if it’s the same thing that I had but :
When I bought The Apple Watch 1 year ago, I cleaned it 2 times a week : this caused me to have a small “infection” just like yours
After that, for the next 11 months, I cleaned the band and the watch almost everyday : no problem since !
Sorry for my bad english