A battery system may include: a master battery processor configured to transmit monitoring commands; and slave battery processors configured to be coupled to batteries, and to transmit battery information of the batteries coupled thereto, to the master battery processor in response to the monitoring commands. The master battery processor determines operation modes of the slave battery processors on the basis of the battery information transmitted from the slave battery processors, and the slave battery processors communicate with the master battery processor at different communication participation rates according to the determined operation modes.