I have only had the Nike+ Series 2 for a couple days, but the battery seems to be slightly better than the Series 1 that I had earlier this year. I'll comment again after a week or so. Yesterday was my first full "normal" day with the watch. I put it on with a full charge at 7:15am. I worked at my desk, checked notifications, used voice & scribble to respond to most, updated my water intake, used maps on my phone which then activated it on my watch (awesome!), and finished off the evening with a run using the Nike+ app to give it a try. I then slept with the watch on to track sleep using AutoSleep. I woke up at 7am with 60% left and charged it while I showered and got ready. I was back to 100% about an hour later. I'd say that same activity left me at about 40-50% on my Series one if I remember correctly. We will see how it goes the rest of this next week.