A battery pack includes a secondary battery, a discharge-control transistor, a charge-control transistor connected in series with the discharge-control transistor between a negative power source terminal of the secondary battery and a terminal of a load or a negative power source terminal of a charger, and a battery protection semiconductor device including a detection circuit that detects at least one of excessively charged, excessive discharging, overcurrent, short-circuit, and overheating states of the secondary battery, a control circuit that turns on and off the discharge-control transistor and the charge-control transistor, and a charge prevention circuit that prevents the secondary battery from being charged by turning off the charge-control transistor when a voltage of the secondary battery is not greater than a predetermined low-voltage criterial voltage variable by trimming a portion of the charge prevention circuit. The charge prevention circuit includes first and second inverter circuits.