A power management system for a portable computer is disclosed. The system can determine which one of a plurality of battery packs has been coupled to the system. After determining the type of battery pack, the system recalls from storage the recommended charging pattern for the particular battery pack and begins to charge the battery at the recommended rate. The system's information is used during charging to determine if the battery pack is defective. When the computer is running off the battery pack, the charge counter measures the total amount of charge supplied to the computer and provides this information to the system. When the difference betweem the total amount of charge supplied to the computer and the total charge available from the battery reaches a predefined limit, the system indicates to the computer that a low-power situation exists and that the computer should prepare for a possible loss-of-power event.