An adapter for a power tool battery. The adapter enables a battery having a first configuration, such as a "slide-on" configuration, to be used with a power tool and/or to be charged by a battery charger having a second configuration, such as a "tower" configuration. The adapter may also enable a battery having one general configuration, such as a "slide-on" configuration or a "tower" configuration, and a first connecting structure to be used with a power tool and/or to be charged by a battery charger having the same general configuration, such as the "slide-on" configuration or the "tower" configuration, respectively, and a second connecting structure different than the first connecting structure.