Until Lightning based chargers are available from other vendors, the folks at UNU have come up with a clever approach. I have used, and enjoyed, their battery pack case for the iphone 4 and 4S, so I was disappointed when I realized there wouldn't be an easy replacement.
So UNU Ecopak built a modular three part system. First, there is a slim, hardshell case that protects your iPhone 5.
The shell is available in multiple colors and has three slots to connect the Ecopak 'battery backpack' that snaps on, securely, and doubles our battery life.
In order to connect the backpack electrically to the iPhone 5, you need to provide your own Lightning cable. Ideally, UNU or someone else will come up with a small (2" or so) cable, to avoid tangles.
The Ecopak is eco-friendly because the battery pack is separate from the case, and can be recycled independently. In fact, they have a promotion where you can get a great deal on the new battery case by sending in an old battery pack to be recycled, or a new hardshell snap case just by liking them on Facebook!
I like that the battery pack is modular, so you could swap out packs indefinitely and always be charged. Just charge the spare packs using the included microUSB cable. All in all, the UNU Ecopak is clever, modular approach to a vexing problem.