Microsoft finally released the Surface Power Cover recently, and it was worth the wait.
There is only one downside: the keys aren’t backlit, like the standard Touch and Type Covers. I can’t imagine why they did this, since the set of people who want significantly more battery life and don’t want a backlighting option has to be pretty small.
Physically, it’s twice as thick and twice as heavy as the standard Type Cover, giving my Surface Pro 2 more of a netbook feel to carry, but not unpleasantly so. It came with a warning label telling you to make sure you have all the latest software updates before attaching it, but since I preordered mine the moment they flipped the switch on the Microsoft site, I got it the day before the official release date, and the firmware updates didn’t show up until the next day. It worked fine, though, and after the update, the battery levels were tracked separately.
How well does it work? Well, I just finished 45 minutes on the elliptical with a ripped Bluray disc playing, at 2/3 volume and 100% brightness, with WiFi turned on. The system reported that I had just over 15 hours of battery life left, and based on how the Pro 2 has performed the past few months, I believe it.