I work second shift. I don't take my AW off the charger until around 10am. When I go to bed around 1 or 2am I still have around 70% battery left. This could easily last the 6 or so hours I sleep. I could then charge the watch in the morning before I go to work. I think the battery is more than capable of monitoring someone's sleep if they are willing to charge it in the morning for a couple hours after they wake up. Hopefully a developer will come out with something here in the future. I really liked jawbones ability to do this.