A battery cell suitable to be used in a battery , comprising: an electrode assembly , comprising a first tab and a second tab with opposite polarities; a casing for accommodating the electrode assembly , wherein the casing comprises a cylinder body and a cover body connected to the cylinder body , the cylinder body is disposed around an outer periphery of the electrode assembly , the cover body is provided with an electrode lead-out hole , and at least part of the cover body is suitable to be used for electrically connecting a first connecting member of the battery and the first tab ; and an electrode terminal for electrically connecting a second connecting member of the battery and the second tab , wherein the electrode terminal is disposed at the cover body in an insulating manner and installed at the electrode lead-out hole , one of the cover body and the electrode terminal is a positive output pole of the battery cell , and the other is a negative output pole of the battery cell ; wherein the cover body and the cylinder body are formed as an integral structure wherein the cover body comprises a connecting portion and a bending portion , the electrode lead-out hole is provided on the connecting portion , at least a portion of the connecting portion is suitable to be used for connecting the first connecting member and the first tab , and the bending portion is used for connecting the cylinder body and the connecting portion ; and characterized in that the bending portion comprises a first end portion for connecting the connecting portion and a second end portion for connecting the cylinder body , and in a direction from the first end portion to the second end portion, a thickness of the bending portion gradually decreases. an electrode assembly , comprising a first tab and a second tab with opposite polarities; a casing for accommodating the electrode assembly , wherein the casing comprises a cylinder body and a cover body connected to the cylinder body , the cylinder body is disposed around an outer periphery of the electrode assembly , the cover body is provided with an electrode lead-out hole , and at least part of the cover body is suitable to be used for electrically connecting a first connecting member of the battery and the first tab ; and an electrode terminal for electrically connecting a second connecting member of the battery and the second tab , wherein the electrode terminal is disposed at the cover body in an insulating manner and installed at the electrode lead-out hole , one of the cover body and the electrode terminal is a positive output pole of the battery cell , and the other is a negative output pole of the battery cell ; wherein the cover body and the cylinder body are formed as an integral structure wherein the cover body comprises a connecting portion and a bending portion , the electrode lead-out hole is provided on the connecting portion , at least a portion of the connecting portion is suitable to be used for connecting the first connecting member and the first tab , and the bending portion is used for connecting the cylinder body and the connecting portion ; and characterized in that the bending portion comprises a first end portion for connecting the connecting portion and a second end portion for connecting the cylinder body , and in a direction from the first end portion to the second end portion, a thickness of the bending portion gradually decreases. <EOS>