A top cover assembly for a battery, wherein the top cover assembly comprises: a top cover, the top cover comprising at least one mounting hole, the mounting hole extending through the top cover in a thickness direction of the top cover, the top cover comprising a first recess on a top surface thereof, the first recess being arranged to surround the mounting hole; a terminal post, the terminal post penetrating the mounting hole, a first end of the terminal post being limited to a side of the top cover on which a bottom surface thereof is located, a second end of the terminal post being higher than the top surface of the top cover; an upper plastic member, the upper plastic member being provided on a side of the top cover on which the top surface is located and surrounding the second end of the terminal post to be connected to the second end of the terminal post, the upper plastic member being provided with a first boss on a bottom surface thereof, the first boss being accommodated in the first recess, the bottom surface of the upper plastic member being located on the top surface of the top cover, wherein the top cover assembly further comprises a lower plastic member, the lower plastic member being provided on the side of the top cover on which the bottom surface thereof is located; the top cover is provided with a second recess on the bottom surface thereof, the second recess is arranged to surround the mounting hole, a second boss matching the second recess is provided at a position of the lower plastic member corresponding to the second recess, and the second boss is accommodated in the second recess; wherein the top cover comprises two mounting holes, and the two mounting holes are located respectively at two ends of the top cover and are symmetrically located with respect to a centerline of the top cover; wherein the top cover is further provided with a liquid injection hole extending through the top cover in the thickness direction of the top cover, and the liquid injection hole is located between the two mounting holes and is offset from the centerline of the top cover; and the top cover is further provided with an explosion-proof through hole extending through the top cover in the thickness direction of the top cover, and the explosion-proof through hole is located between the two mounting holes and located on the centerline of the top cover, characterized in that, wherein an area of a projection of the first recess on the top surface of the top cover is smaller than an area of a projection of the second recess on the top surface of the top cover, and a volume of the first recess is the same as a volume of the second recess, and wherein a sum of areas of the mounting holes, the liquid injection hole and the explosion-proof through hole is S1, and a total area of the top cover is S, 0 < S1/S ≤ 0.2. a top cover, the top cover comprising at least one mounting hole, the mounting hole extending through the top cover in a thickness direction of the top cover, the top cover comprising a first recess on a top surface thereof, the first recess being arranged to surround the mounting hole; a terminal post, the terminal post penetrating the mounting hole, a first end of the terminal post being limited to a side of the top cover on which a bottom surface thereof is located, a second end of the terminal post being higher than the top surface of the top cover; an upper plastic member, the upper plastic member being provided on a side of the top cover on which the top surface is located and surrounding the second end of the terminal post to be connected to the second end of the terminal post, the upper plastic member being provided with a first boss on a bottom surface thereof, the first boss being accommodated in the first recess, the bottom surface of the upper plastic member being located on the top surface of the top cover, wherein the top cover assembly further comprises a lower plastic member, the lower plastic member being provided on the side of the top cover on which the bottom surface thereof is located; the top cover is provided with a second recess on the bottom surface thereof, the second recess is arranged to surround the mounting hole, a second boss matching the second recess is provided at a position of the lower plastic member corresponding to the second recess, and the second boss is accommodated in the second recess; wherein the top cover comprises two mounting holes, and the two mounting holes are located respectively at two ends of the top cover and are symmetrically located with respect to a centerline of the top cover; wherein the top cover is further provided with a liquid injection hole extending through the top cover in the thickness direction of the top cover, and the liquid injection hole is located between the two mounting holes and is offset from the centerline of the top cover; and the top cover is further provided with an explosion-proof through hole extending through the top cover in the thickness direction of the top cover, and the explosion-proof through hole is located between the two mounting holes and located on the centerline of the top cover, characterized in that, wherein an area of a projection of the first recess on the top surface of the top cover is smaller than an area of a projection of the second recess on the top surface of the top cover, and a volume of the first recess is the same as a volume of the second recess, and wherein a sum of areas of the mounting holes, the liquid injection hole and the explosion-proof through hole is S1, and a total area of the top cover is S, 0 < S1/S ≤ 0.2.