Buy.com has the Cables Unlimited BatteryBoost for iPhone 3G and 3GS for $34.49 with Free Shipping.
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- 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.