I read reports that beta users were getting great battery life under 3.1. I wasn't prepared for how big the improvement would be. I have a Series 1, and I had 75% battery left after 16 hours yesterday. After charging it over night, I have 97% battery after 6 hours. This is with everything turned on like location services and background app refresh. So far I haven't had any strange reboots like I had under 3.0. I would say this is an amazing update for the watch.