Gomadic High Capacity Rechargeable External Battery Pack suitable for the Apple iPhone 4S Integrated circuitry tailors output voltage and charging current to exact specification of the Apple iPhone 4S (accurate to 0.1v). Specification: Internal Battery (7800mAh lithium polymer), Input port (microUSB), Output Port (Standard USB), Onboard Circuit Design (Apple iPhone 4S Specific), Dimensions (2.75 X 3.25 X 0.75 inches), TipExchange enabled (Yes) Very easy to operate. Simply connect Apple iPhone 4S, press activation button on pack, and charging begins. Quick start guide included. Designed with a front facing LED display that clearly display the current battery capacity at the touch of a button Internal circuit protects the Apple iPhone 4S from various power ailments including surges, overcharging and short circuiting. Advanced logic maximizes charger efficiency