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Around 2 months. I have a genius appointment Monday since the Apple stores are opening again. Wish they would swap it instead of sending it off though. I fear they will say it is OK like they did on the phone :-(

Good luck. Mine started turning around in February. It’s been smooth sailing since then. I really didn’t want to send it off with COVID just beginning.
 
So the Genius Bar kindly give me a brand new watch instead of sending it off and waiting. Time will tell if the battery works on this one. The heart rate monitor in activities never worked properly either on my other one plus the strap was too tight when trying to attach it to the watch. So because i have 3 problems they replaced it. :)
 
Series 5, 44 mm. I usually get around 36 hours until I drop to under 10% and have to charge. Right now I have 28 hours on with 25% left. This is AOD except during sleep when I have it in Theater mode with DND turned on.
 
Mine has gone back to being bad again. If I go for an hours walk by 9-10pm it is dead.

I've also noticed that mine is getting worse. About 20% left at the end of the day when it used to be around 40%. Nothing really changed, so I'm not sure what happened. Thinking about having Apple do a diagnostic. Maybe I'll get lucky and be below 80%.
 
Yeah I don’t know what it is. But I think it but be doing a lot work the first few weeks you have it. Then it levels out. But keep in mind I don’t workout. I use it mostly for communication and for notifications. I mostly use my watch to viewing info rather than actually doing things on/with it. I do use Siri and Walkie-Talkie a lot. Also, keep in mind I’m still in lockdown so my usage isn’t what it would normally be.
 
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