A method for charging multiple battery packs is disclosed, which comprises the steps of providing full output power of the power conversion unit to a first battery pack in a charging cycle at the control of a first control signal; monitoring in real-time the charging acceptance of the first battery pack and when the charging acceptance detected is less than the available full output power of the power conversion unit, charging a second battery pack by the remaining output power, i.e. the output power difference between the full available output power and the charging acceptance of the first patent pack, at the control of a second control signal. The service life of battery is extended and the efficiency of the PV module is increased in the system where in the method is implemented. A device for charging multiple battery packs is also disclosed.