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I was having severe drain on both my watch and 12 mini. I unpaired my watch (watch was on watchOS 8.0 and phone on 15.0.2), let it sit for a few days, during which 15.1 came out, then, repaired, updated to watchOS 8.1, and battery on both seems to be back to normal. Screenshots of before/after (screenshot taken Sat 1:11pm):
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Went from ~12hrs to ~36hrs battery life.
 
Wellll.... somewhere between watchOS 8 and 8.3 this issue just went away. That is until today when I upgraded to 8.4 around 2pm. It's now 9:40pm and I just received the dreadful low power alert Apple sometimes... lol
 
8.4 is catastrophic on my Series 6! I lost 50% in 4 hours, doing 30 mins cycling and sitting at my desk for the rest of the time.
 
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