A cordless system has cordless system components that include a cordless device, such as a cordless power tool, a battery pack and a charger. The battery pack is mated with either the cordless device to provide power to operate the cordless device or to the charger to charge the battery cells in the battery pack. In an aspect of the invention, the cordless system has an identification and communication system by which the battery pack identifies and communicates information about the battery pack to the cordless device or to the charger to which the battery pack is mated. In another aspect of the invention, the battery pack of the cordless system is capable of multiple modes, such as controlling the cordless device and controlling the charger. In yet another aspect of the invention, the battery pack validates the cordless device or charger to which it is mated. In still another aspect of the invention, the cordless system uses any of a wired interface, radio frequency interface, an optical interface or a magnetic interface to communicate information between the battery pack and the cordless device or charger to which the battery pack is mated.