I've had mine 8 full days now (received 8am on 4/24) and I haven't once yet come close to depleting the battery. I wear it 6:30am to 12:30am daily, and it's nearly never dropped below 30% for me. Maybe once it hit 25%. And that's with a lot of emails and iMessages.
I take it off and charge it while I sleep. I wouldn't wear a conventional watch to sleep, either, so it's been no different.
Battery life is of no concern to me. The battery indicator is no longer one of my displayed complications.
I wear mine to sleep. Ever since I had a Fitbit, then a Pebble and then Fitbit Surge I've been wearing my watch/fitness tracker on the weekdays to bed so I can wake up at 4:30am to hit the gym. I'm married now and don't want to set a loud alarm and wake her up too. When I was single I needed 2 alarms to wake me up, one set on the Radio and one set on a loud beeping alarm. The vibrating/tapping on my wrist is a good change that works 90% of the time.