Powerful Lithium Polymer Rechargeable Gomadic Brand Battery Pack High Capacity Portable Charger Compatible with Garmin etrex 10 20 30 with upgradeable TipExchange Technology Very easy to operate. Simply connect Garmin etrex 10 20 30, 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 (Garmin etrex 10 20 30 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 Garmin etrex 10 20 30 (accurate to 0.1v). Built with high capacity lithium polymer rechargeable battery technology (28 Wh / 7800 mAh) in a compact design. Designed with a front facing LED display that clearly display the current battery capacity at the touch of a button