A battery charging system includes two or more rechargeable batteries, a charging power supply charging the batteries with an external electrical power, a charging power sensing part sensing at least one of a voltage and a current of a charging power supplied from the charging power supply to the batteries, and a charging control part controlling the charging power supply to supply an idle power created during charging one battery, to another battery according to a sensed result of the charging power sensing part. With this configuration, a charging time of the two or more batteries is reduced, and the electrical power is efficiently used when the two or more batteries are charged.