Those multifunctional gadgets are always welcome such as the following iPhone case called MiLi Power Skin.
This multifunctional iPhone case is manufactured by HALI-POWER, a China-based manufacturer. MiLi Power Skin features ultra slim design, but the material used by the iPhone case doesn’t described on its product page. Moreover, it integrates a 1200mAh rechargeable battery that can be charged through the built-in USB port.
MiLi Power Skin can be fit for iPhone 3G/3GS, and is available in various colors. However, there is no further word on the release date and the price at iPhoneMili. Well, stay tuned.
Alternatively, you also can check out another similar iPhone case, or more eco-friendly solar powered iPhone case.
Update: Now the MiLi Power Skin iPhone battery case has been available. Through Google Shopping find the most suitable one.