Patent ID: 8018205

Claim:
A multi battery pack system including a master battery pack and a plurality of slave battery packs, wherein the master battery pack receives a total voltage from each slave battery pack and calculates a target total voltage using a total voltage of the master battery pack and total voltages of all slave battery pack whenever a predetermined time period passes, sends the calculated target total voltage to each slave battery pack, compares the target total voltage with the total voltage of the master battery pack, and then connects or disconnects a cell group of the master battery pack and output terminals according to the comparison result; and wherein the slave battery packs include at least one slave battery pack, which sends a total voltage of the slave battery pack according to a request of the master battery pack, receives a target total voltage from the master battery pack, compares the target total voltage with the total voltage of the slave battery pack, and then connects or disconnects a cell group of the slave battery pack and output terminals according to the comparison result.