Nilay Patel at The Verge:
13 hours and 29 minutes. That’s all you really need to know — that’s how long the new MacBook Air running Safari lasted running The Verge Battery Test, which cycles through a series of websites and images at 65 percent brightness. Run time in Chrome was shorter, at 11 hours and 29 minutes, but both are still ridiculously impressive. In fact, it’s the record for a laptop running our test without an external battery.
I wasn’t expecting a Retina display, but I wasn’t expecting this kind of battery life increase, either. While the machine’s base clock speed is slower than the previous model, reviewers have claimed that the slight change isn’t noticeable. I’d say the mid–2013 MacBook Air is a winner.