In my battery tests, where I turn off all power-saving features, crank the screen brightness up all the way, leave the Wi-Fi on, and play a continuous loop of music, they fell well short of that.
In my tough laptop test, where I turn off power-savings software, crank up the screen to 100%, leave the Wi-Fi on to collect email, and play a continuous loop of music, the XPS 12 lasted just 3 hours and 31 minutes.