A battery charger with an improved battery retention system is provided. The battery charger includes at least one pocket having a bottom and sidewalls. A pair of battery engagement rails, or coupling rails, extends outward into the pocket at an angle that is non-orthogonal with the sidewalls. These non-orthogonal rails, which may include embedded electrical contacts, mate with non-orthogonal female slots in a battery pack housing. The non-orthogonal angle prevents lateral forces applied to the battery from causing intermittent electrical connections between the battery pack and the charger. Additionally, the non-orthogonal angle of the rails allows batteries of various sizes to be inserted into the pocket while ensuring a consistent and reliable electrical connection.