The savings are arrestingly simple: Redesigning a standard pumping loop in one factory saved 92% of the pumping power--with lower construction cost and better performance.

FORBES: The Case For Efficiency

In my test, where I use full brightness, disable power-saving software, leave on the Wi-Fi, and play a loop of music, the battery on the XPS 13 lasted just under four hours, the worst I've seen on an ultrabook.

WSJ: Walt Mossberg: Dell's Slim, Speedy Ultrabook Fits Anywhere, but Loses Steam

My test taxes the computer more than a normal user and involves keeping Wi-Fi on, cranking the screen to full brightness, turning off all power-saving features, keeping email retrieval going in the background and playing an endless loop of music.

WSJ: A Laptop Screen That Promises an Eyeful