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 . <EOS>