Started at 6AM - By 11PM it was at 26%.
Turn off the fitness monitor and activity tracking, and power saving under the heart rate, and you'll get a lot better battery.
Well I got my watch a week ago tonight and of course cannot count the first day but the other days were all 15 hour days and the percentage at the end of the day ran from 52% at the lowest to 57%. It will be interesting to see if the amount decreases. But After the first day I found i did not like have notifications for my emails, I get far too many in a day for one of my email accounts for work and check it hourly on my phone. I am actually quite happy with it so far.
I start the day around 6 a.m. recharging the watch somewhere between 80–100% and wear it all day—and even to bed. When I wake up the next morning it'll be down to 30–40% with 24 hours of standby and a several hours of usage.