The battery charging system allows a power consumption of an information processing apparatus to be maximally reduced when the system is off. When a charge request signal is output from a microprocessor of one battery, a connection control circuit puts one switch circuit into a open state and the other switch circuit into a closed state. As a result, a Smart Selector operates to start charging the battery whose connection has been detected. When the battery is fully charged and a full charge signal which is an inverted version of a charge request signal is output from the microprocessor, the connection control circuit operate to open the closed switch circuit and to close the opened switch circuit. The Smart Selector is made to recognize that the battery is no longer connected and detects only the other battery, thereby beginning charging to the other battery.