I sent my Series 5 into the repair center (well, my Apple Store sent it there) and it bounced back from them after a couple days, saying they couldn't replicate the problem. They were useless. It's like the Apple Watch falls into this gulch, as far as Apple support goes. It's the only thing they can't try to fix in the store, at their own Genius Bar. And they weren't that happy with the Apple repair center either. Before I read about the turn it off for 15 min and then back on again, I had literally tried every single thing except getting a new watch (which the store said I couldn't get, since Apple Care didn't cover a repair when they couldn't find the problem). But I've read about people here who got new ones and it didn't help the problem. I've restored from previous, from scratch, put it in the freezer (worked a couple days), taken it to the Genius Bar three times and talked to support in Cupertino (I pay $500 a year for Joint Venture Business Support) and the only consistent thing I ever got was that it was a software issue. No updates ever helped. My previous four Apple Watches, each of the series, didn't have this problem. But then I did the 15 min off and back on (I can't remember how much it was already charged when I did that. I think I did it when it had said 100% for 24 hours and I knew it would in the next 6 hours just randomly die. I haven't had any problems since then and that's been around 2-3 months ago that I did it. If anything, it uses up the battery a tiny bit faster than it used to.