Apple Watch will only last 2.5 hours with heavy use
According to 9to5mac, the Apple Watch the battery is looking at just 2.5 to 4 hours of "active application use" before it dies. Granted, most people aren't going to be full-on using it as their primary device... but I could certainly see people dorking around for 2.5 hours on the thing.
"As a point of comparison, the Moto 360 easily lasts a full day of mixed-use. Our own Eric Limer's watch still had a little under half of its battery left after about 16-hours of wear. Even the Samsung Gear S, which is essentially a full-fledged phone for your wrist, can go a full day easy. And of course, the Pebble Smartwach, which is admittedly a very different beast, can last close to a full week on a single charge." - http://goo.gl/0qXCQ8