It contains two parts of charger and battery pack. 1 charger also contains adapter (Adaptor) and charging controller two parts. The adapter converts AC power to DC power, and the charge controller limits the maximum current and maximum voltage of the DC. 2 The battery pack contains two parts of the protection board and the battery core, and a PTC to limit the maximum current. Adapter AC to DC function: power controller current limit voltage limit. Charger function: Protection board overcharge, over discharge, over current protection.