The Dell XPS 13 features a four-cell, 7.4 V, 52 Wh battery with "up to 11 hours of run time."

That's 11 hours of web browsing, with "system brightness set to 150 nits (40%) and wireless on"—highly dependent on personal configuration and usage.

Usage reports vary pretty wildly on the functional battery life.

For comparison: Apple's Early 2014 MacBook Air claims 12 hours of web browsing or iTunes movie playback on its 54 Wh battery.