I have a Series 2 42 mm and I easily get 2 days of use on a charge. My last charge was yesterday morning off the charger at around 9:30 am. As of 1:30 pm today (28 hours of use) and I still have 64% charge. One thing I do is set the brightness to minimum and turn off Activate on Wrist Raise when I go to bed. These save loads of battery for the next day. I also have a red color minimalistic modular watch face that I use if I want to really extend the battery. With OLED screens the less pixels turning on, the less power needed. But I mostly don't bother switching the face since I don't really have battery issues.Apple is going to make my nightly ritual a little easier in the next version with a "Theater Mode" which turns off the Activate on Wrist Raise with a single button on the swipe from the bottom control panel.