BATTERY PACK CHARGING METHOD, BATTERY PACK AND POWER SOURCE DEVICE

A battery is charged to an ideal capacity to prolong the charging and discharging cycle life of the battery. A pack battery charging method is a charging method for connecting pack battery (10) to charger (20) and charging pack battery (10) at a constant voltage and a constant current. Pack battery (10) detects a degree of deterioration of battery (11) and a supply voltage at which charger (20) charges pack battery (10), and specifies a charging termination current from both the supply voltage of charger (20) and the degree of deterioration of battery (11) to perform charging.