A system for managing a battery, the system comprising: one or more switches configured to connect a battery and a load; a voltage measuring unit configured to measure a voltage value of the battery; a control unit configured to control the one or more switches based on the measured voltage value; and a communicating unit configured to transmit the measured voltage value to the control unit; a reference voltage generating unit which is configured to be connected with the battery in parallel and is configured to generate a reference voltage, wherein the voltage measuring unit, the one or more switches, and the communicating unit are formed as a battery disconnecting unit, BDU, and the control unit is positioned outside the BDU, wherein the BDU is configured to be positioned at the battery side, and the control unit is configured to be positioned at the load side, wherein the reference voltage generating unit is configured to generate a first reference voltage for diagnosing overcharging of the battery module and a second reference voltage for diagnosing overdischarging of the battery module; wherein the control unit is configured to diagnose a state of the battery module based on the first reference voltage, the second reference voltage, and the voltage value of the battery module measured by the voltage measuring unit; wherein the communicating unit further includes: an insulating unit configured to electrically insulate the measured voltage value from the first and second reference voltages generated by the reference voltage generating unit; and a transmitting unit configured to transmit the electrically insulated voltage value to the control unit. one or more switches configured to connect a battery and a load; a voltage measuring unit configured to measure a voltage value of the battery; a control unit configured to control the one or more switches based on the measured voltage value; and a communicating unit configured to transmit the measured voltage value to the control unit; a reference voltage generating unit which is configured to be connected with the battery in parallel and is configured to generate a reference voltage, wherein the voltage measuring unit, the one or more switches, and the communicating unit are formed as a battery disconnecting unit, BDU, and the control unit is positioned outside the BDU, wherein the BDU is configured to be positioned at the battery side, and the control unit is configured to be positioned at the load side, wherein the reference voltage generating unit is configured to generate a first reference voltage for diagnosing overcharging of the battery module and a second reference voltage for diagnosing overdischarging of the battery module; wherein the control unit is configured to diagnose a state of the battery module based on the first reference voltage, the second reference voltage, and the voltage value of the battery module measured by the voltage measuring unit; an insulating unit configured to electrically insulate the measured voltage value from the first and second reference voltages generated by the reference voltage generating unit; and a transmitting unit configured to transmit the electrically insulated voltage value to the control unit.