While this could change the game for electric cars (Edit: as others have already been discussing), it would also be an amazing advance for cell phones and computers. Imagine a cell phone that had a lighter battery but still lasted through a week of use between charges. Or an incredibly thin and light battery (and a correspondingly thin and light phone) that still lasted a couple of days.

Or a notebook that didn't need all the power management to dial down the CPU and GPU when unplugged, and could barrel away full speed and still last for a day or two. You'd still have to worry about heat dissipation, but there are plenty of fast notebooks that handle that fine when plugged in.

Or an iPad with the battery life of a Kindle. Or a Kindle that you charged once a year.