The Augment case from Rubix is currently a Kickstarter campaign that will go into full production, but offers a different take on the battery case for the iPhone 5 and 5s. The Rubix Augment case, brings a new tasteful and minimalist design, while offering protection for the iPhone from drops and allows for connectivity to the Augment battery pack.
https://www.kickstarter.com/projects/rubixco/augment