I know many have been talking about the Mophie juice pack air and incase etc. for battery packs Honestly the best iPhone external battery pack I have found is the PhoneSuit Mili power pack. It's 2000Mah first of all. More than any of the other comprable solutions. I dont count the fastmac because that thing is just horribly ugly and huge. The Mili styling is nice, very iphone friendly and it includes a USB out port to charge any device. The thickness is virtually the same as the juice pack air. It is longer on the bottom due to the ports, but its not a big deal. I mean thats not much for nearly twice the power of the mophie. It has a slide on design which I love, because who wants a battery permanently attached to your phone? Just use it when you need it. Anyway, let me know what you guys think.
http://www.phonesuit.com/products/Mi...ack-14-10.html