A battery management system (BMS) includes at least one sub-BMS and a main BMS. The at least one sub-BMS measures information about a battery, and generates an activation signal according to operating state. The main BMS receives the activation signal and determines the operating state of the at least two sub-BMSs. If the at least two sub-BMSs normally operate, the main BMS generates a synchronization signal and transfers the same to the sub-BMSs. The at least one sub-BMS measures the information about the battery according to the synchronization signal.