3GJuice takes a different approach to external power. Rather than a case-style battery, 3GJuice is a square dongle that attaches via a dock connector. It’s less convenient to use—making the iPhone somewhat awkward to carry and use while plugged in—but on the plus side, the 1800mAh 3GJuice will probably work with your existing case, not to mention any other iPhones or iPods you already have. The compact battery sports a green LED to indicate that it’s charging, but there’s no way to tell how much power the 3GJuice has left.
As one of the most compact external batteries we’ve seen, its size makes this battery an appealing option for travelers or users who don’t want a battery integrated into a case.
Dongle-style battery works with iPods or iPhones. Compact.
Makes the iPhone awkward to use while charging. No way to gauge remaining power. 
