Gomadic Portable AA Battery Pack designed for the HTC EVO 4G - Powered by 4 X AA Batteries to provide Emergency charge. Built using TipExchange Technology Built using the unique Gomadic TipExchange Technology that protects your investment by providing the ability to upgrade charging ports by simply swapping physical connectors. Specification: Input Voltage (4 X AA Batteries), Cable length (6 inches), Dimensions (5.0 X 1.5 X 0.75 inches), Circuit Design (HTC EVO 4G specific), TipExchange enabled (Yes) Integrated circuitry regulates output voltage specific to the HTC EVO 4G. Advanced logic maximizes overall charger efficiency. Easy to operate. Simply insert batteries, toggle on/off switch and your HTC EVO 4G will start to charge. A must have accessory for the frequent traveler, camper or heavy HTC EVO 4G user.