A battery pack charging system includes a battery pack interface configured to receive a battery pack, a charging circuit coupled to the battery pack interface to provide charging current to the battery pack interface, and a controller coupled to the charging circuit and configured to control supply of charge current to the battery interface. The battery pack charging system further includes a power supply circuit coupled to the charging circuit, a filter circuit coupled to the power supply circuit and including a nanocrystalline ferrite common mode choke, and an alternating current plug configured to connect the filter circuit to an alternating current power source.