A battery charging system is disclosed. The battery charging system includes a battery charger, a switching circuit and a control circuit. The battery charger receives electric power from a DC power supply and charges a rechargeable battery based on a setting current. The switching circuit is capable of switching between a first charging mode and a second charging mode. In the first charging mode, the battery charger charges the rechargeable battery while the DC power supply is supplying electric power to the battery charger in a state where the DC power supply is able to supply electric power to a load. In the second charging mode, the DC power supply charges the rechargeable battery in a state where the DC power supply is able to supply electric power to the load. The control circuit controls the switching circuit based on a comparison result of the magnitude of a charging current (or a charging power) in the first charging mode and the magnitude of a charging current (or a charging power) in the second charging mode.