The present invention provides an improved method for detecting the state of charge (SOC) of a battery. A remaining capacity detection circuit detects the SOC of a rechargeable battery. A coulomb counter circuit integrates the charge and discharge currents IBAT of the battery to generate a coulomb count value CC. A voltage detection circuit detects a voltage VBAT of the battery. An SOC calculation unit calculates a raw SOC value SOC_cc based on the coulomb count value CC. A discharge correction unit corrects the raw SOC value SOC_cc based on a voltage drop of the battery during the discharging of the battery, and generates a discharge SOC value SOC_dis. A charge correction unit measures a minimum value SOC_dis_min reached by the discharge SOC value SOC_dis during the last discharge of the battery, and calculates a charge SOC value SOC_chg using the minimum value SOC_dis_min during the charging of the battery.