12 hours is the reported life, but I bet that's with constantly fiddling with it. The device's battery life is probably proportional to how often the screen is kept on and CPU fully awake.
In real world usage, after the initial geek factor expires, the device will probably last longer. I've certainly had that experience with the other Android Wear watches and Google Glass.
I'd also expect the upgrade to Android L to improve battery life.
"One of the cool things about Android Wear smartwatches so far has been the always-on dimmed mode, so you can always flip up and see what time it is. The Moto 360, however, doesn't roll that way. When the screen's not on, the screen's not on. The one exception is when it's on the dock, charging." - http://www.androidcentral.com/moto-360-hands-redux
That's on top of the dimmed display. It runs in the dimmed power save mode, but when you "flick" the watch towards you (slightly exaggerated movement compared to a normal glance at a watch) it turns up and accepts voice commands (at least on the G).
My Pebble battery life went through the roof a few weeks after I got it, when I stopped loading all new apps several times a day and fiddling with it. Once I found apps I liked and settled into a routine, it went from 1 day to 5 days.
In real world usage, after the initial geek factor expires, the device will probably last longer. I've certainly had that experience with the other Android Wear watches and Google Glass.
I'd also expect the upgrade to Android L to improve battery life.