US Patent 9136729 Power tool battery pack wireless charger

A power tool system includes a power tool, a power tool battery pack and a battery pack charger. The power tool battery pack is separable from and attachable to the power tool, and electrically connectable to the power tool electrical terminals when attached to the power tool. The power tool battery pack has at least one battery cell, a receiver coil, and a control circuit for controlling the amount of power that is provided to the at least one battery cell. The battery pack charger has at least one transmitter coil for generating a magnetic field which induces a voltage in the receiver coil, and a control circuit for controlling the amount of power that is provided to the transmitter coil.