Power supply apparatus and method of controlling the same

A power supply apparatus (16) includes a controller (36). If the controller (36) detects that the internal resistance of a battery (20) detected by an internal resistance detecting unit (28) is relatively high, then the controller (36) switches a first switch (22) from an open state to a closed state using a first threshold value with respect to the voltage difference between a battery voltage and a system voltage, and if the controller (36) detects that the internal resistance of the battery (20) is relatively low, then the controller (36) switches the first switch (22) from the open state to the closed state using a second threshold value which is smaller than the first threshold value.