Battery pack and motor-driven tool using the same

A battery pack comprises a housing including an upper housing with an opening, and a lower housing with a lower surface at an opposite side of the opening, side walls extending in a substantially longitudinal direction, and end walls extending in a substantially transverse direction; wherein a plurality of lithium-ion battery cells are positioned in the housing and arranged in parallel with the lower surface, a circuit board is disposed in the housing and electrically connected to the lithium-ion battery cells; a plurality of terminals including a positive terminal, a negative terminal and a signal communicating terminal are arranged in a direction perpendicular to the longitudinal direction of the side walls, and each terminal includes an engaging portion adjacent to the opening, and a connecting portion is electrically connected to the circuit board; and a protecting portion is positioned between the engaging portion and the lithium-ion battery cells and engaged to the upper housing to protect against foreign matter from contacting the plurality of lithium-ion battery cells and the circuit board through the opening.