A battery system includes: a charging circuit comprising a bidirectional charger and a main processor; and a plurality of battery packs, wherein each of the plurality of battery packs comprises a battery cell and a battery processor, wherein the main processor is configured to transmit, by using the bidirectional charger, to the battery processor of each of the plurality of battery packs, a charging signal to charge the battery cell of each of the plurality of battery packs, wherein the battery processor is configured to: based on receiving the charging signal, sequentially perform constant current (CC) charging of each of the plurality of battery packs according to a predefined order, and based on the CC charging of the plurality of battery packs being completed, simultaneously perform constant voltage (CV) charging of each of the plurality of battery packs.