It's just 12 hours of video playback that they actually cite when selling the thing (wifi locked to a network and autobrightness off, all else default). That's nice and similar to other high-end devices like a MBP, but it's so powerful that if you actually do the things on it that you'd want to buy a high-powered device for (e.g. editing video, gaming, 3d modelling) you won't last anywhere near that.

In short, if you use it like a tablet, you get typical tablet battery. If you have it docked to the stand to use the dedicated GPU etc, I assume you're going to get more typical windows laptop battery life. But that's not much different from my MBP either, I usually get about 5-6 hours of battery life rather than 10-12 because I use it a lot for the things I actually needed to buy a MBP for, which isn't just watching video and checking my mail.

My hunch is both halves have a battery. Also that 12 hours is listed as video playback, which is not how Apple measures.