Provided in the embodiments of the present application are an end cap assembly, a battery cell, a battery and an electric device. The end cap assembly comprises an end cap and a pressure relief member, wherein the end cap is provided with a recess portion sunk towards the interior of the battery cell, and the pressure relief member is arranged in the recess portion; and the distance between a top surface of the pressure relief member that deviates from the interior of the battery cell and the recess bottom of the recess portion is less than or equal to the depth of the recess portion. Therefore, the pressure relief member does not protrude from the top surface of the end cap, and the pressure relief member does not additionally occupy the space of the battery cell in a height direction. On the premise that the total height of the battery cell is not changed, the interior space of the battery cell using the end cap assembly is larger, so that more pole pieces can be accommodated in the battery cell, and thus the active substance capacity of the battery cell can be increased, thereby improving the energy density of the battery cell.