The battery used in the 1928-31 Model A Ford is listed as a 6 volt, positive grounded type, with a “Ford MADE IN U.S.A.” logo appearing on one side of the battery case. Although it is called a three-cell 6 volt battery, each cell is really 2.1 volts each. It was easier for people to remember they have a 6 volt battery rather than a 6.3 volt battery. The battery case was made of a rubber composition material. The location of the battery posts were changed when the late 1928-31 batteries were introduced, allowing Ford to shorten the negative cable from 22-27 inches to 18 inches per car, saving production costs. To read more click the link How it works