The battery management system (BMS) measures a state of charge (SOC) of a battery by using a total amount of charge corresponding to a total amount of discharge accumulation. The BMS, outputting a SOC of a battery to an engine control unit (ECU), includes a sensor, state of health (SOH) and SOC measurers, a total amount of charge (TAC) determiner, and an output unit. The sensor detects a pack current and a pack voltage of the battery. The SOH measurer outputs a SOH of the battery by using the pack current and voltage. The SOC measurer measures a SOC of the battery by using the pack current and a TAC of the battery. The TAC determiner accumulates a total amount of discharge accumulation by using the pack current, determines a TAC corresponding to the total amount of discharge accumulation, and delivers the determined TAC to the SOC measurer. The output unit outputs the SOC and SOH to the ECU.