STANDBY POWER SUPPLY DEVICE AND METHOD FOR CHARGING SECONDARY BATTERY

The standby power supply device includes one or more secondary batteries and a charging circuit that charges the secondary batteries. The charging circuit includes a voltage adjuster that controls the state of charge of the secondary batteries, and a controller that controls the voltage adjuster by detecting the degree of deterioration of the secondary batteries over time. In the charging circuit, the voltage adjuster charges the secondary batteries at a charge voltage lower than a full charge voltage of the secondary batteries to bring the secondary batteries into a load power supply standby state, and gradually increases the charge voltage of the secondary batteries according to the degree of deterioration of the secondary batteries detected by the controller.