A battery bar is a small metal bar that is used to interconnnect individual cells in the homebuilt construction of a racing-type battery pack, since many matched cells are sold as a disassembled set. They are usually copper and often gold- or silver-plated to aid in current flow.
Battery bars are soldered between the terminal of each cell in series, thereby multiplying the voltage of the finished pack. Soldering ensures maximum conductivity. By comparison, the cells in pre-assembled "sport packs" are connected with thin strips of metal which are spot-welded to the terminals of each cell. As a result, the current is greatly reduced since it can only flow at the pinprick-sized welds as opposed to a larger solder joint.
Some years ago, Trinity Corporation created a still-popular line of battery bars called "Lennon Lugs," so named because the circular contacts joined by a horizontal bar greatly resembled the round, "hippie" eyeglasses often worn by musician and composer John Lennon.