"There are literally hundreds, if not thousands of smartphone covers and cases on the market, but probably none as functional as the one I am going to tell you about now. You sometimes see almost every second person in a group with an iPhone 4 and they personalise it more times than not with a case of their preference.
What you rarely see, though, are folks getting around with powered cases. What we are looking at today is an iPhone 4 case that comes with a built-in 2000mAh battery. It's from a relatively new company called PowerSkin and they claim to provide twice the amount of power with their iPhone 4 silicone case using patented XPAL Power technology."