A battery module comprising first and second battery bodies (1, 2), wherein each of the first and second battery bodies (1, 2) includes two connecting terminals (13, 14) of different polarities, the first battery bodies and the second battery bodies are arranged alternately such that the polarities of the connecting terminals (13, 14) of each adjacent pair thereof are different from each other, each first battery body is constituted by a first battery holder and a first battery cell, which is held by the first battery holder, each second battery body is constituted by a second battery holder and a second battery cell, which is held by the second battery holder, each first battery cell includes a first protrusion on a terminal surface, on which the connecting terminals (13, 14) are provided, each second battery cell includes a second protrusion on a terminal surface, on which the connecting terminals (13, 14) are provided, wherein the second protrusion does not face any of the first protrusions in an arrangement direction of the battery cells (11, 12), each first battery holder includes a first projecting portion, wherein, when an attempt is made to fit the second battery cell to the first battery holder, the first projecting portion contacts the second protrusion, thereby preventing the second battery cell from being accommodated in the first battery holder, and each second battery holder includes a second projecting portion, wherein, when an attempt is made to fit the first battery cell to the second battery holder, the second projecting portion contacts the first protrusion, thereby preventing the first battery cell from being accommodated in the second battery holder. each of the first and second battery bodies (1, 2) includes two connecting terminals (13, 14) of different polarities, the first battery bodies and the second battery bodies are arranged alternately such that the polarities of the connecting terminals (13, 14) of each adjacent pair thereof are different from each other, each first battery body is constituted by a first battery holder and a first battery cell, which is held by the first battery holder, each second battery body is constituted by a second battery holder and a second battery cell, which is held by the second battery holder, each first battery cell includes a first protrusion on a terminal surface, on which the connecting terminals (13, 14) are provided, each second battery cell includes a second protrusion on a terminal surface, on which the connecting terminals (13, 14) are provided, wherein the second protrusion does not face any of the first protrusions in an arrangement direction of the battery cells (11, 12), each first battery holder includes a first projecting portion, wherein, when an attempt is made to fit the second battery cell to the first battery holder, the first projecting portion contacts the second protrusion, thereby preventing the second battery cell from being accommodated in the first battery holder, and each second battery holder includes a second projecting portion, wherein, when an attempt is made to fit the first battery cell to the second battery holder, the second projecting portion contacts the first protrusion, thereby preventing the first battery cell from being accommodated in the second battery holder.