A battery management system for managing a battery including a plurality of battery cells and a driving method are provided. The system includes a sensor, and a main control unit (MCU). The sensor senses a voltage and a current of the battery. The MCU receives the voltage and the current of the battery, measures an open circuit voltage (OCV) in key-on using the battery voltage, and estimates an initial SOC depending on the OCV in the key-on. The MCU divides the OCV into first and second OCV regions, and, when the OCV in the key-on is in the first OCV region, estimates the initial SOC using a linear equation.