A battery cap assembly, comprising: a cap plate including a first terminal hole; a first electrode terminal provided to the cap plate and extending into the first terminal hole; and a first connecting piece provided below the cap plate; wherein the first connecting piece includes a first connecting portion connected with the first electrode terminal, the first electrode terminal includes a first protruding portion and a first base portion, the first protruding portion protrudes above the cap plate, the first base portion is connected with the first connecting piece and extends into the first terminal hole, and a cross-sectional area of the first protruding portion is larger than a cross-sectional area of the first terminal hole, the first electrode terminal further includes a boss, the boss extends downwardly from a lower surface of the first base portion, characterized in that the cap plate is made of insulating material; an upper surface of the first connecting portion is attached to the cap plate; the first connecting portion includes a first fitting hole; the boss extends into the first fitting hole; the lower surface of the first base portion is attached to the upper surface of the first connecting portion. a cap plate including a first terminal hole; a first electrode terminal provided to the cap plate and extending into the first terminal hole; and a first connecting piece provided below the cap plate; wherein the first connecting piece includes a first connecting portion connected with the first electrode terminal, the first electrode terminal includes a first protruding portion and a first base portion, the first protruding portion protrudes above the cap plate, the first base portion is connected with the first connecting piece and extends into the first terminal hole, and a cross-sectional area of the first protruding portion is larger than a cross-sectional area of the first terminal hole, the first electrode terminal further includes a boss, the boss extends downwardly from a lower surface of the first base portion, characterized in that the cap plate is made of insulating material; an upper surface of the first connecting portion is attached to the cap plate; the first connecting portion includes a first fitting hole; the boss extends into the first fitting hole; the lower surface of the first base portion is attached to the upper surface of the first connecting portion. the first connecting piece includes a first connecting portion connected with the first electrode terminal, the first electrode terminal includes a first protruding portion and a first base portion, the first protruding portion protrudes above the cap plate, the first base portion is connected with the first connecting piece and extends into the first terminal hole, and a cross-sectional area of the first protruding portion is larger than a cross-sectional area of the first terminal hole, the first electrode terminal further includes a boss, the boss extends downwardly from a lower surface of the first base portion, characterized in that the cap plate is made of insulating material; an upper surface of the first connecting portion is attached to the cap plate; the first connecting portion includes a first fitting hole; the boss extends into the first fitting hole; the lower surface of the first base portion is attached to the upper surface of the first connecting portion.