Gomadic High Capacity Rechargeable External Battery Pack suitable for the Amazon Kindle Fire / Fire HD Very easy to operate. Simply connect Amazon Kindle Fire / Fire HD, press activation button on pack, and charging begins. Quick start guide included. Specification: Internal Battery (7800mAh lithium polymer), Input port (microUSB), Output Port (Standard USB), Onboard Circuit Design (Amazon Kindle Fire / Fire HD Specific), Dimensions (2.75 X 3.25 X 0.75 inches), TipExchange enabled (Yes) Integrated circuitry tailors output voltage and charging current to exact specification of the Amazon Kindle Fire / Fire HD (accurate to 0.1v). Built using unique Gomadic TipExchange Technology that protects your investment by providing the ability to upgrade charging ports by simply swapping the physical connector. Built with high capacity lithium polymer rechargeable battery technology (28 Wh / 7800 mAh) in a compact design.