A battery pack, a battery charger, a method for charging a battery pack are provided. The battery pack includes a secondary battery, a switch element for controlling charging and discharging the secondary battery, a controller for controlling the switch element, and a communication unit for performing with a battery charger. During charging, an initial charging is switched to a quick charging when a voltage of the secondary battery reaches a predetermined voltage, and the battery charger judges the battery pack as abnormal when the voltage does not reach the predetermined voltage within a timeout period after the initial charging is started. At least one of the timeout period and the predetermined is stored. At least one of the timeout period and the predetermined voltage to be read out is transmitted through the communication unit to the battery charger.