The present disclosure discloses a battery management system that uses a small number of opto-couplers to reduce a production cost. The battery management system is controlled to maintain a turn-off state in a normal condition. Also, switches are connected in series, and the switches are connected such that when any one switch turns on, switches connected subsequent to the turned-on switch turn on in sequential order. The turn-on of the last connected switch causes a switch turning on an opto-coupler to be turned on. As a result, when the opto-coupler turns on, a battery management device may transmit information to an external device.