A battery pack, comprising: a housing; a battery pack interface enabling the battery pack to be detachably connected to a power tool, wherein the battery pack interface comprises a battery pack positive terminal and a battery pack negative terminal; and a cell assembly located in the housing, wherein the cell assembly comprises a plurality of non-cylindrical cells (241, 241a, 241b), a cell assembly positive terminal and a cell assembly negative terminal for outputting electric energy from the cell assembly; a positive lead-out piece, wherein the positive lead-out piece connects the cell assembly positive terminal to the battery pack positive terminal; a negative lead-out piece, wherein the negative lead-out piece connects the cell assembly negative terminal to the battery pack negative terminal; wherein a discharge path is formed by the cell assembly positive terminal, the positive lead-out piece, the battery pack positive terminal, the cell assembly negative terminal, the negative lead-out piece, and the battery pack negative terminal and configured to supply power to the power tool; and a protective element disposed on the discharge path, wherein the protective element is configured to turn off the discharge path to disconnect the discharge path when a discharge current through the discharge path is greater than or equal to a preset current, characterized in that either, the protective element is connected between the positive lead-out piece and the battery pack positive terminal; and a length of the positive lead-out piece close to the protective element is greater than a length of the negative lead-out piece away from the protective element; or, the protective element is connected between the negative lead-out piece and the battery pack negative terminal; and a length of the negative lead-out piece close to the protective element is greater than a length of the positive lead-out piece away from the protective element. a housing; a battery pack interface enabling the battery pack to be detachably connected to a power tool, wherein the battery pack interface comprises a battery pack positive terminal and a battery pack negative terminal; and a cell assembly located in the housing, wherein the cell assembly comprises a plurality of non-cylindrical cells (241, 241a, 241b), a cell assembly positive terminal and a cell assembly negative terminal for outputting electric energy from the cell assembly; a positive lead-out piece, wherein the positive lead-out piece connects the cell assembly positive terminal to the battery pack positive terminal; a negative lead-out piece, wherein the negative lead-out piece connects the cell assembly negative terminal to the battery pack negative terminal; wherein a discharge path is formed by the cell assembly positive terminal, the positive lead-out piece, the battery pack positive terminal, the cell assembly negative terminal, the negative lead-out piece, and the battery pack negative terminal and configured to supply power to the power tool; and a protective element disposed on the discharge path, wherein the protective element is configured to turn off the discharge path to disconnect the discharge path when a discharge current through the discharge path is greater than or equal to a preset current, characterized in that either, the protective element is connected between the positive lead-out piece and the battery pack positive terminal; and a length of the positive lead-out piece close to the protective element is greater than a length of the negative lead-out piece away from the protective element; or, the protective element is connected between the negative lead-out piece and the battery pack negative terminal; and a length of the negative lead-out piece close to the protective element is greater than a length of the positive lead-out piece away from the protective element.