A battery module , comprising: - a housing ; - a plurality of battery cells disposed in the housing ; and - a bus bar configured to electrically couple two adjacent battery cells of the plurality of battery cells , wherein the bus bar comprises: - a first end coupled to a first terminal of a first battery cell of the plurality of battery cells , wherein the first end is formed from a first material, and wherein the first end comprises a first collar extending from a lower surface of the bus bar configured to receive and surround the first terminal ; - a second end coupled to a second terminal of a second battery cell of the plurality of battery cells , wherein the second end is formed from a second material, and wherein the second end comprises a second collar extending from the lower surface of the bus bar configured to receive and surround the second terminal , wherein the first and second materials are different materials, and wherein the lower surface of the bus bar faces the first battery cell and the second battery cell , when the bus bar is electrically coupled to the first terminal and the second terminal ; and - a joint disposed between the first end and the second end , wherein the joint mechanically and electrically couples the first end to the second end , wherein the joint comprises a rolled finger joint. - a housing ; - a plurality of battery cells disposed in the housing ; and - a bus bar configured to electrically couple two adjacent battery cells of the plurality of battery cells , wherein the bus bar comprises: - a first end coupled to a first terminal of a first battery cell of the plurality of battery cells , wherein the first end is formed from a first material, and wherein the first end comprises a first collar extending from a lower surface of the bus bar configured to receive and surround the first terminal ; - a second end coupled to a second terminal of a second battery cell of the plurality of battery cells , wherein the second end is formed from a second material, and wherein the second end comprises a second collar extending from the lower surface of the bus bar configured to receive and surround the second terminal , wherein the first and second materials are different materials, and wherein the lower surface of the bus bar faces the first battery cell and the second battery cell , when the bus bar is electrically coupled to the first terminal and the second terminal ; and - a joint disposed between the first end and the second end , wherein the joint mechanically and electrically couples the first end to the second end , wherein the joint comprises a rolled finger joint. - a first end coupled to a first terminal of a first battery cell of the plurality of battery cells , wherein the first end is formed from a first material, and wherein the first end comprises a first collar extending from a lower surface of the bus bar configured to receive and surround the first terminal ; - a second end coupled to a second terminal of a second battery cell of the plurality of battery cells , wherein the second end is formed from a second material, and wherein the second end comprises a second collar extending from the lower surface of the bus bar configured to receive and surround the second terminal , wherein the first and second materials are different materials, and wherein the lower surface of the bus bar faces the first battery cell and the second battery cell , when the bus bar is electrically coupled to the first terminal and the second terminal ; and - a joint disposed between the first end and the second end , wherein the joint mechanically and electrically couples the first end to the second end , wherein the joint comprises a rolled finger joint. <EOS>