The HP Compaq nc4000 Battery with Travel Pack powers the HP Compaq nc4000 Notebook while in the office or on the road. Using a 6-Cell Lithium Ion Battery, the HP Compaq nc4000 Battery with Travel Pack offers you an extra 3.5 hours of battery life. When used with the travel pack and primary battery, the battery provides up to 7 hours of power. The same pack is used internally in the notebook and in the travel pack for greater flexibility. The HP Compaq nc4000 Battery with Travel Pack can charge one battery at a time using a 6-Cell Lithium Ion Battery. The 65 W AC adapter provides a constant voltage to the charger. The charger also has a calibration feature that detects when the battery should be calibrated for optimal battery life.