Brilliant... in the thickness of the hard case, the BatteryBoost has a rechargeable battery doubling the autonomy of your iPhone 3G or iPhone 3GS. Simply slide your iPhone 3G or iPhone 3GS into the BatteryBoost and gain a couple of hours "of battery" life. Plug your original charger cable into the BatteryBoost to charge your device and the extra battery at the same time.
No need to use extra cables, BatteryBoost snaps on to your device
BatteryBoosts battery is the most powerful of the market: 2400 mA