US Patent 9520738 Inductive charging device for a battery device

A charging system for a battery device of a handheld tool includes a charging device provided to inductively charge the battery device in a charging operation, the charging device having at least one induction charging unit which has at least one charging coil having a main coil extension. A gap is provided between the battery device and the charging device in a charging operation. A ratio between (i) the at least one main coil extension and (ii) a minimum clearance between the at least one charging coil and a surface defining the gap is at most 30/1.