A NiH/NiCd (nickel hydrogen/nickel cadmium) battery charger with the function of emergency power supply unit having a main body with a charging chamber and a charging circuit positioned within the main body to allow an electric connection to the charging chamber and the power input interface. This charging control circuit is controlled by an electrical switch which divides the charging chamber into two or more parts. When the power input interface is connected, the electrical switch shuts off automatically to make the batteries in the charging chamber to be charged in groups. This is the function of charger. When the power input interface is switched off, the batteries in different circuit are joined in series to supply power as an emergency power supply unit. Therefore, with the design principle of "separate charging and common sharing", it can protect the rechargeable batteries and provide power in lacking of power supply unit outdoors.