The batteryl ife was fine in watchOS 1 and 2 and 3 beta 1 and 2, but in watchOS3 beta 3 it dies 3 1/2 hours after being 100% full.
I updated the Apple Watch to watchOS 3 beta 3 and now it dies a few hours after being fully charged
Try turning off the "Hey Siri" feature. It saved me a lot of battery life.
I had this problem also, but after unpairing then repairing the watch my watch battery life has been great. I have no idea why it worked but hey its worth a try.
I think it has something to do with the new watch faces. Try to charge your AW to 100% and choose a "simple" old watch face for some time and watch the battery percentage.
Martin
Yeah, this worked for some reason, thanks.