A battery pack includes first and second pack terminals, a battery between first and second battery terminals, a main switch between the first pack terminal and the first battery terminal, a first resistor and a first insulated switch in series between the first battery terminal and a ground, a second resistor and a second insulated switch in series between the second battery terminal and the ground, and a controller to control the first and second insulated switches to alternately repeat a first state, in which the first insulated switch is closed and the second insulated switch is opened, and a second state, in which the first insulated switch is opened and the second insulated switch is closed, detect a first terminal voltage, control the main switch, and determine whether the main switch malfunctions based on a difference between the first terminal voltage in the first and second states.