Estimates like this are tough, because it’s not at all obvious how people will actually use the watch. Apple, the report says, is wringing 2.5 hours out of the watch in heavy application use, and about 3 hours if the watch face is displayed continuously. The thing is, no one is likely to use the watch that way. Think about it: you probably look at your watch way less than you check your phone, and when you do, you don’t stare at it and play with it for minutes on end. Watches are made for glancing at, and screens take up vast amounts of energy.
For mixed use, Apple is finding, they’re getting 19 hours a day. Not great, but probably just enough to be credible. Barely.
Ship date now seems to be the end of March.