I just returned my second Series 6 because of an unanswered battery issue.
My wife and I bought watches together. Both series 6. Both came loaded with ios7.
Hers works great and after a full day of about 14 hours, she still has at least 50% battery left. My watch, even set exactly like hers goes completely dead after 6 hours.
I made sure the settings of the two watches were exactly the same - no differences. She uses hers more than I use mine.
I unpaired mine, re-paired, no change.
I paired my watch to her phone for a day and it got better, but still not what she's getting.
I did a total reset on my phone, full erase and reset. Paired as a new watch again and... no change.
I have iPhone Xs
My wife has iPhone X
Same carrier, same network, pretty much same settings.
Took the second watch back to the store today as I can't waste anymore days on this issue that Apple needs to fix. They wanted me to try one more. Really? You're wanting me to believe I not only bought a lemon to begin with, but the replacement I bought was also a lemon? If that's the case, I don't want this product!
Anyway, I love the device but until they fix this, I'm not buying another one.
Cheers