A lower plastic assembly configured to be assembled with an upper cover and comprising a first lower plastic member and a second lower plastic member arranged side by side at one side of the upper cover in a length direction of the end cover assembly, with the second lower plastic member abutted against the first lower plastic member, the first lower plastic member and the second lower plastic member being stacked with the upper cover, and a sum of a length of the first lower plastic member and a length of the second lower plastic member being equal to a length of the upper cover, wherein the first lower plastic member comprises a first-lower-plastic-member body, wherein the first-lower-plastic-member body further comprises a first upper surface and a first lower surface, and the first upper surface is opposite to the first lower surface; the first-lower-plastic-member body defines a first liquid-injection through-hole, wherein the first liquid-injection through-hole extends through the first-lower-plastic-member body and is located at one end of the first-lower-plastic-member body, a cutout is defined at one side of the first liquid-injection through-hole and is in direct communication with the first liquid-injection through-hole, and the cutout extends through the first upper surface and the first lower surface; and the first lower plastic member further comprises a recess, wherein the recess is recessed from the first upper surface and has a lower wall and a peripheral wall surrounding the lower wall, and the first liquid-injection through-hole extends through the lower wall; the cutout extends through the first upper surface and the first lower surface in a direction from the first upper surface to the first lower surface and extends through part of a wall surface of the peripheral wall; the first lower plastic member comprises a first grid, wherein the first grid comprises a connecting portion and defines a plurality of first gaps at one side of the connecting portion, the connecting portion comprises a guiding slope inclined towards the plurality of first gaps, the cutout is located between the connecting portion and the first liquid-injection through-hole, and the cutout extends through part of the guiding slope. the first lower plastic member comprises a first-lower-plastic-member body, wherein the first-lower-plastic-member body further comprises a first upper surface and a first lower surface, and the first upper surface is opposite to the first lower surface; the first-lower-plastic-member body defines a first liquid-injection through-hole, wherein the first liquid-injection through-hole extends through the first-lower-plastic-member body and is located at one end of the first-lower-plastic-member body, a cutout is defined at one side of the first liquid-injection through-hole and is in direct communication with the first liquid-injection through-hole, and the cutout extends through the first upper surface and the first lower surface; and the first lower plastic member further comprises a recess, wherein the recess is recessed from the first upper surface and has a lower wall and a peripheral wall surrounding the lower wall, and the first liquid-injection through-hole extends through the lower wall; the cutout extends through the first upper surface and the first lower surface in a direction from the first upper surface to the first lower surface and extends through part of a wall surface of the peripheral wall; the first lower plastic member comprises a first grid, wherein the first grid comprises a connecting portion and defines a plurality of first gaps at one side of the connecting portion, the connecting portion comprises a guiding slope inclined towards the plurality of first gaps, the cutout is located between the connecting portion and the first liquid-injection through-hole, and the cutout extends through part of the guiding slope.