Battery cell, battery, and electrical device

A battery cell, comprising:

• a case with an opening;
• an electrode assembly accommodated within the case;
• and
• an end cover closing the opening,
• wherein the end cover is in sealed connection with the case through a first connection area and a second connection area along a circumferential direction of the end cover, the strength of the first connection area is less than the strength of the second connection area, and the first connection area is configured to be actuated to release an internal pressure of the battery cell when the internal pressure exceeds a threshold;
• and
• wherein, along the circumferential direction of the end cover, a third connection area is further provided between the first connection area and the second connection area, and the strength of the third connection area gradually decreases from a connection position between the third connection area and the second connection area to a connection position between the third connection area and the first connection area, the minimum strength of the third connection area is not less than the strength of the first connection area, and the maximum strength of the third connection area is not greater than the strength of the second connection area.