A battery management system and a method of operating the same includes a plurality of battery cells constituting one pack and connected to a battery having at least one pack, and determines an estimated state of charge (SOC) of the battery. The battery management system determines whether or not a pack current flows, and controls a reset of an SOC depending on the determination result. The battery management system sets an OCV idle period associated with a temperature of the battery, and compares the idle period with a time for which the current of the battery does not flow, and sets the reset OCV depending on the comparison result. The battery management system resets the estimated SOC as the reset SOC associated with the reset OCV.