Well guys, I did it... I reset my iPhone settings (this automatically causes the watch to unpair and reconnect with the phone). It's been 4 hours and the battery went from 85% down to 66%. But I did a 45 min. workout and used the watch quite a bit. So I lost 19% in 4 hours. That's about 4,75% per hour but including a workout.
This morning I lost 35% in 6 hours - that was nearly 6% per hour without working out or doing anything.
So maybe I'm on the track back to a decent battery life.
But as a heavy Apple user since 2005 (MacBooks, iPods, the first iPhone in 2007...) I've never expereinced such bad software before... it seems like it's getting worse.
EDIT: Wow... and battery drain is back! Lost 10% in the last 30 minutes! This sucks. I'm about to throw this ****** watch away.