A battery rack includes: a plurality of battery packs; a plurality of slave battery management systems, each of the slave battery management systems being coupled to a corresponding one of the battery packs, being powered by an operating power, and being configured to use the corresponding one of the battery packs for the operating power in response to receiving a corresponding one of a plurality of operating power changing signals; and a master battery management system coupled to the slave battery management systems and configured to transmit the operating power changing signals to the slave battery management systems.