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 either a terminal of a load or a negative power source terminal of a charger, and a battery protection semiconductor device for protecting a secondary battery. The battery protection semiconductor device includes a detection circuit that detects at least one of an excessively charged state, an excessive discharging state, an overcurrent state, a short-circuit state, and an overheating state 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.