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 , 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 , 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 . <EOS>