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 . <EOS>