The present disclosure discloses a top cover assembly of battery and top cover assembly, the top cover assembly comprising: a top cover having first recess on top surface, the first recess is provided around mounting hole; a terminal post penetrating mounting hole, first end of terminal post is limited to a side of top cover on which a bottom surface is located, second end of terminal post is higher than top surface of top cover; an upper plastic member provided on a side of top cover where top surface thereof is located and surrounding second end of terminal post to be connected to second end of the terminal post, the upper plastic member has a first boss on a bottom surface, the first boss is accommodated in the first recess, the bottom surface of the upper plastic member is connected to the top surface of the top cover.