I have had two of these units and, whilst the concept is great and they work well initially, both of them have failed in the same way. The USB connector works loose and disappears inside the unit making it useless. Mophie do have a one year warranty but don't seem prepared to honour it. Suggest you steer well clear of this.
I too have owned 2 Mophie Juice Packs and both have had faulty USB connectors, one dissapeared inside, the other completely removed itself with my USB chargeing cable snapping the internal ribbon cable from the unit. In both cases, Mophie have REFUSED to honour their stated 12 month warranty. They have no dedicated customer support management and are completely disrepectful in the process. DO NOT BUY MOPHIE PRODUCTS UNLESS YOU JUST WANT TO BURN CASH