Gomadic Advanced Apple iPhone 3G compatible AA Battery Pack Charge Kit &ndash; Portable power built with upgradeable TipExchange Technology Integrated circuitry regulates output voltage specific to the Apple iPhone 3G. Advanced logic maximizes overall charger efficiency. Specification: Input Voltage (4 X AA Batteries), Cable length (6 inches), Dimensions (5.0 X 1.5 X 0.75 inches), Circuit Design (Apple iPhone 3G specific), TipExchange enabled (Yes) Built using the unique Gomadic TipExchange Technology that protects your investment by providing the ability to upgrade charging ports by simply swapping physical connectors. Safely engineered with reverse polarity protection, in the event batteries are accidentally put in incorrectly. Internal circuit designed to protect your Apple iPhone 3G from power surges, overcharging and short circuiting.