AppleWatch Series 5 Nike+ GPS. Watch OS6.0.1. Only had my watch for one week and the battery drain is horrible (compared to Series, 1,2,3,4). I opened a case with Apple Support the same day as the watch was received. Turning off the "always on" feature seemed to help. However, the screen remained somewhat dimly lit. I have brightness set to the maximum. I have done the suggested (here on this thread) reset. No change in the drain. At 5pm yesterday, the watch was fully charged. I did normal activities and took it off at 10pm. By 6am, the watch had drained to 64%! Within the past 2 days, the watch is now extremely slow to charge. From 64% to 95% takes 1 hour 20 minutes. Crazy.
I was back with a supervisor in AppleSupport this morning who has made an appointment for me to return/exchange the watch on Tuesday at an Apple Store 55 miles away. Worst release of an Apple product EVER (Apple user since 1984).