A battery pack includes a secondary battery including a plurality of cell blocks, a measuring section, a charge and discharge control switch, a protection circuit, and a memory. The measuring section detects a voltage, a current, and an internal resistance, of the secondary battery. The controller monitors the voltage and the current of the secondary battery and outputs a request signal indicative of a charge condition to charge the secondary battery in accordance with the charge condition which is set. The protection circuit monitors voltages of the plurality of cell blocks. The memory registers an initial internal resistance of the secondary battery. The controller calculates a deterioration coefficient by a ratio of the internal resistance detected by the measuring section to the initial internal resistance registered in the memory, and changes the charge condition in accordance with the deterioration coefficient.