Tekkeon myPower Rechargeable Battery Case with Replaceable Battery Module for AT&T/Verizon iPhone 4/4S - Black Delivers power for hours of extra play/work time through an innovative bypass that preserves the iPhone 4 battery by powering, not charging, your iPhone 4 eSwap technology lets you swap the battery module on the go to double, triple, or more, the amount of power you get with myPower for iPhone 4. Optional ultra Ultra slim profile gives power without unnecessary bulk Ultra slim profile gives power without unnecessary bulk High-speed micro USB 2.0 interface lets you automatically sync your iPhone 4 Preserves iPhone 4 Battery: Preserves the iPhone battery by bypassing the battery and directly powering (rather than charging) iPhone 4. Swappable Battery Module: Features Tekkeon's new innovative eSwap technology that lets you easily use a fresh battery module. Highly Efficient Design Provides Maximum Power: Intelligent circuitry provides an unheard of 95% efficiency for maximum power output, without adding substantial weight or size to iPhone 4. Complete Protection from Wear and Tear: Doubles as a protective case with raised edges to provide a high level of protection. Included myGuard protection films for iPhone 4 prevent dust or other elements from scratching the surface. Increases Comfort: With a sleek contour that softens the iPhone 4 edges, and a slip-proof soft touch finish, myPower for iPhone 4 makes iPhone 4 more comfortable to hold