The XTAR BC4 battery charger was designed to charge batteries of standard AA (AA) and remote control (AAA) batteries. Can be used for 1.5 V Li-ion, 1.2 V Ni-MH and Ni-CD type batteries. (Not compatible with 3.6/3.7V Li-ion batteries!) The smart charger is actually four units that operate independently of each other, it automatically recognizes the inserted batteries and the required charging method, and even charges different types at the same time, up to 4 pcs. AAA, 4 AA, 2 AA and 2 AAA, or only 2 AA or 2 AAA batteries can be charged at the same time. The charge level is indicated by the LEDs on the top of the charger. It detects the full charge of the cells and completes the charge, thereby preventing overcharging. The charger is protected against reverse polarity, short circuit, overload and overheating. BC4 can also be used as a power bank with charged batteries (in this case, the manufacturer recommends AA batteries of the same type, capacity and brand!)