A battery pack includes: a plurality of batteries including a first battery and a second battery; a first input/output port including a first input/output positive port and a first input/output negative port; a second input/output port including a second input/output positive port and a second input/output negative port; a first switch electrically connecting the positive terminal of the second battery to the negative terminal of the first battery or to the second input/output positive port; a second switch electrically connecting the negative terminal of the first battery to the first switch or to the first input/output negative port; and a third switch electrically connecting the negative terminal of the second battery to the first input/output negative port or electrically connecting the second switch to the first input/output negative port or to the second input/output negative port.