POWER SUPPLY DEVICE AND POWER SUPPLY CONTROL METHOD

To provide a power supply device and a power supply control method with which charging and electric power supply can be continued efficiently, and a charge capacity can be added. A power supply device including: plural battery units replaceably connected to a battery connection part, an output unit for outputting electric power from the battery unit to a load, and a control unit for controlling connection of the plural battery units with respect to the output unit, wherein the control unit selects a battery unit having a remaining charge amount that is smallest among the plural battery units and equal to or greater than a first predetermined amount, and connects the selected battery unit to the output unit.