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.