Being able to get through the work day is generally the battery life target in today's laptops and ultrabooks. Many can handle a good six hours of light Web browsing, but heavier workloads can seriously ramp up battery drain. We tested the XPS 12 with Battery Eater Pro, which chews through laptop batteries as fast as possible, and our own Web browsing test, in which we refresh a webpage until the battery is depleted.
Given how thin the XPS 12 is, we didn't expect it to last an exceptionally long time untethered to a power outlet. Still, it managed to last nearly as long as the Surface Pro 3 in the Battery Eater Pro test, petering out after 155 minutes of constant CPU hammering.
In our custom battery rundown test, which loops a web page while keeping screen brightness at 50%, the XPS 12 eked out 6.5 hours of usage. That's fairly close to Dell's stated 8 hours, and those who crank the brightness down or engage in less constant browsing could likely hit that mark.