Interesting that myself, friends and family, not to mention the people on threads here have had such rotten luck.
My 26 month old Apple Watch S5 battery health:
The first Watch I had for 3 months lost 5% battery health in that time. My colleagues launch day S5 is on 79% and dies by the evening. Mine now lasts all day with AOD disabled but won’t make it past 19:30pm when enabled. If it’s nothing at all to do with this feature, why is the performance directly affected whether it’s on or off?
I’m sure the iPhone version will be better, however my experience with 2 watches using AOD hasn’t been the most positive.