Abstract: This invention includes a battery pack having an improved battery retention system for coupling to another device, like a desktop charger. The battery pack, which includes one rechargeable cell and optional circuitry, has an exterior housing that is generally rectangular in cross section. The exterior housing, which includes major faces and intersection seams, has at least two female slots that project inward at an angle that is non-orthogonal to the major faces or intersection seams. These non-orthogonal slots, when coupling to corresponding non-orthogonal rails in the pocket of a battery charger, allow batteries of various sizes to be inserted into a single charger pocket with reliable and consistent electrical connections between the electrical contacts of the pocket and the charging terminals of the battery. Electrical contacts may be disposed within the non-orthogonal slots, thereby improving both the function and aesthetic appearance of the battery pack.