The invention relates to a battery group and an electrode current piece thereof. The electrode current piece of the battery group comprises at least two electrode connection parts which are connected electrically with the electrodes located at the same side of the corresponding single battery cells in the battery group. All the electrode connection parts are connected together electrically through electrode current pieces. At least one electrode connection part comprises a butt welding connection piece electrically connected by welding with the electrode of the corresponding single battery cell and conductive ring pieces placed on the outer circle of the butt welding connection piece in regular intervals. The conductive ring piece and the electrode current piece body are connected electrically. The butt welding connection piece and the conductive ring pieces are connected electrically through a conductive arc arm. The conductive arc arm has an over-current fusion part. The butt welding connection piece and the conductive ring pieces are connected through the conductive arc arm. Moreover the conductive arc arm has the over-current fusion part. In the application the butt welding connection piece is connected electrically by welding with the electrode of the corresponding single battery cell. When the over-current condition appears at the single battery cell, the over-current fusion part fuses to cut off the current for protection.