A battery pack, comprising: a multi cell assembly comprising a plurality of bare cells (111, 113), the multi cell assembly defining opposing planar surfaces; a protection circuit at one side of the multi cell assembly, the protection circuit comprising: a protection circuit board including a first connector, defining a notch and/or hole, comprising a long connector (121a_1) and a short connector (121a_2) having a length less than the long connector (121a_1), and a first lead terminal and a second lead terminal electrically connecting the multi cell assembly to the protection circuit board, and wherein the battery pack further comprises: a holder between the multi cell assembly and the protection circuit, the holder including a second connector, comprising a protrusion, coupled to the first connector; a case surrounding a periphery of the multi cell assembly and the protection circuit and exposing the opposing planar surfaces of the multi cell assembly to an exterior of the multi cell assembly; and the multi cell assembly further comprising reinforcing tape attached to the opposing planar surfaces. a multi cell assembly comprising a plurality of bare cells (111, 113), the multi cell assembly defining opposing planar surfaces; a protection circuit at one side of the multi cell assembly, the protection circuit comprising: a protection circuit board including a first connector, defining a notch and/or hole, comprising a long connector (121a_1) and a short connector (121a_2) having a length less than the long connector (121a_1), and a first lead terminal and a second lead terminal electrically connecting the multi cell assembly to the protection circuit board, and wherein the battery pack further comprises: a holder between the multi cell assembly and the protection circuit, the holder including a second connector, comprising a protrusion, coupled to the first connector; a case surrounding a periphery of the multi cell assembly and the protection circuit and exposing the opposing planar surfaces of the multi cell assembly to an exterior of the multi cell assembly; and the multi cell assembly further comprising reinforcing tape attached to the opposing planar surfaces. a protection circuit board including a first connector, defining a notch and/or hole, comprising a long connector (121a_1) and a short connector (121a_2) having a length less than the long connector (121a_1), and a first lead terminal and a second lead terminal electrically connecting the multi cell assembly to the protection circuit board, and wherein the battery pack further comprises: a holder between the multi cell assembly and the protection circuit, the holder including a second connector, comprising a protrusion, coupled to the first connector; a case surrounding a periphery of the multi cell assembly and the protection circuit and exposing the opposing planar surfaces of the multi cell assembly to an exterior of the multi cell assembly; and the multi cell assembly further comprising reinforcing tape attached to the opposing planar surfaces. a holder between the multi cell assembly and the protection circuit, the holder including a second connector, comprising a protrusion, coupled to the first connector; a case surrounding a periphery of the multi cell assembly and the protection circuit and exposing the opposing planar surfaces of the multi cell assembly to an exterior of the multi cell assembly; and the multi cell assembly further comprising reinforcing tape attached to the opposing planar surfaces.