ELECTRICAL POWER SUPPLY SYSTEM, MOVING OBJECT, CONTROL METHOD, AND STORAGE MEDIUM

An electrical power supply system includes: an estimation unit capable of estimating a first residual capacity, which is a residual capacity of a first electrical power storage device, based on an amount of electrical power charged and discharged by the first electrical power storage device; and an update control unit which, in a state in which, by controlling a first connection device, a second electrical power storage device is connected via a first connection circuit and a second electrical power supply circuit to a first electrical power supply circuit, is capable of disconnecting the first electrical power storage device from the first electrical power supply circuit by controlling a first disconnection device, and is capable of updating a first residual capacity estimated value, which is the first residual capacity estimated by the estimation unit, based on an open circuit voltage of the first electrical power storage device.