I'll just chime in here that I have noticed similar behavior. I have two series 6 watches that I alternate between, the battery health is listed as 83%. Yesterday was the first day I noticed a significant battery runtime change with both watches. The previous day both watches were running around 14 hours including an hour of workout mode. Now the watches go from fully charged to empty in about 6-7 hours without an hour of workout. ( However, did seem to survive 7-8 hours in sleep mode with about 25% drain. ) Software wise the only change was the iOS 17.4 update that I installed the previous evening. There have been no watch updates in that time.