A power supply system for supplying power to a load of an electronic apparatus includes first and second battery units, and a selector coupled to the load and the first and second battery units. The selector is operable so as to break electrical connection between the second battery unit and the load and to simultaneously make electrical connection between the first battery unit and the load when a remaining capacity of the first battery unit is higher than a predetermined reference value, and so as to break electrical connection between the first battery unit and the load and to simultaneously make electrical connection between the second battery unit and the load when the remaining capacity of the first battery unit is lower than the predetermined reference value. A controller coupled to the selector, is responsive to a first control command, which may be issued by the electronic apparatus, so that the controller overrides the detector and enables operation of the selector in the first state.