A Burgess battery was a specialized dry cell battery that was marketed to professionals such as electronic engineers, and to companies and government departments that wanted to buy massive numbers of batteries.
The Burgess Battery Company was founded by Charles F. Burgess in 1917 at a plant in Madison, Wisconsin, and later moved to Freeport, Illinois. The company was in business for several decades, but by the 21st century, the company became a subsidiary of Honeywell, and had discontinued battery production, as the heavy metals in their battery formula were found to be too hazardous for the employees. Burgess made thousands of customized batteries during the 20th century for which there were no replacement.
Since he had used them in his experiments and previous jobs, Emmett Brown chose two oversized Burgess batteries as fresh replacement batteries for the walkie talkies that were originally bought by his future self in 1985A, in preparation for Marty's trip to 1885.