If you open the watch app on the iPhone and check the usage, does it have a lot of usage when you are down to 20% or so? Just checking to see if a bad third party app might be constantly talking to the phone. Maybe empty the dock for awhile and see if it helps. Same for complications. Only use Apple ones for awhile. These are just ideas. Some say disable SOS. Others say re-pair the watch.Don't know what I'm doing wrong but I can't get my watch to last longer than 7 hrs before it's dead completely.
watchOS 3 beta 3