In more normal use, with power-saving on, I suspect you could get 4 to 5 hours on the XPS 12, but that's still nothing to write home about.

WSJ: Review of Dell XPS 12: Dell Laptop Does Flips to Try to Be a Thick Tablet

Still, these are respectable numbers in my harsh tests, and suggest to me that in more normal use with power-saving on, you could get six hours or so easily on these machines.

WSJ: Ultrabooks Bring Light and Speedy to Windows

The AMD Radeon HD 8000M Series features AMD Enduro Technology, a cutting-edge power-saving solution that scales GPU usage and power based on graphics demand.

ENGADGET: AMD Radeon HD 8000 series GPUs official for laptops, desktop series now shipping to OEMs