Integrated circuitry tailors output voltage and charging current to exact specification of the Sony Walkman NWZ-S638F (accurate to 0.1v). Very easy to operate. Simply connect Sony Walkman NWZ-S638F, 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 (Sony Walkman NWZ-S638F Specific), Dimensions (2.75 X 3.25 X 0.75 inches), TipExchange enabled (Yes) Built with high capacity lithium polymer rechargeable battery technology (22.2 Wh / 56000 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 No more scoping out airport waiting rooms for AC plugs. No more sweating in the parking lot waiting for your Sony Walkman NWZ-S638F to charge. Keep the family plugged in on camping trips or the office wondering how you are always so utterly available. Small, Lightweight and extremely durable, the Gomadic High Capacity Battery Pack for the Sony Walkman NWZ-S638F is the perfect addition to any nomads road arsenal. Whether you need an extra boost to squeeze some extra hours out of the Sony Walkman NWZ-S638F or you are resurrecting it from the dead, the High Capacity Battery keeps you mobile, agile and free. Consider yourself an independent and free-moving provider of energy!

Integrated circuitry tailors output voltage and charging current to exact specification of the Sony Walkman NWZ-S638F (accurate to 0.1v). Very easy to operate. Simply connect Sony Walkman NWZ-S638F, 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 (Sony Walkman NWZ-S638F Specific), Dimensions (2.75 X 3.25 X 0.75 inches), TipExchange enabled (Yes) Built with high capacity lithium polymer re