Just finished up my first (work) day with my Series 3 watch and I'm incredibly impressed with the battery life. I was very excited with the prospect of a watch with cellular connectivity because I'm not allowed to carry my phone at work (NDA/no cameras). Being able to stay connected all day sounded great but I was worried about the battery life. I'm happy to report however that after a full 18 hours of usage, 9 of which being cellular, I'm going to bed with the battery at 40% remaining. That's about 25% more left in the tank than my Series 0 would leave me with. To be fair, I'm not the heaviest user. I only received a couple dozen messages and emails throughout the day with no phone calls on the watch and other than that I only really used it to check the time, weather, calender, activity, and some reminders. Still, I think it's great they managed to make the LTE modem so power efficient.