Charger having non-orthogonal coupling rails

A battery charger (705) with an improved battery retention system is provided. The battery charger (705) includes at least one pocket (700) having a bottom (706) and sidewalls (707-709). A pair of battery engagement rails, or coupling rails, (701, 704) extends outward into the pocket (700) at an angle that is non-orthogonal with the sidewalls (707-709). These non-orthogonal rails (701, 704), which may include embedded electrical contacts, mate with non-orthogonal female slots (407, 408) in a battery pack housing (400). The non-orthogonal angle prevents lateral forces applied to the battery from causing intermittent electrical connections between the battery pack (400) and the charger (705). Additionally, the non-orthogonal angle of the rails (701, 704) allows batteries of various sizes to be inserted into the pocket (700) while ensuring a consistent and reliable electrical connection.