I have a 38mm Watch. I updated to the latest software and battery life is amazing. Been wearing the watch for 8 hours and battery is at 93%. I think previously when I'd get home from work the battery would be maybe 70-75%. I'm going to use it at the gym tomorrow I'll be curious to see if anything changes there. How great would it be to be able to use it at the gym and wear it all day/evening without having to charge in between.