At the Chunky Baptist Church??

Early editions of the ANSI standard used a letter code to identify the dimensions of the cell. Since at the time there were only carbon-zinc cells, no suffix letters or other notation were required. The letter system was introduced in the 1924 edition of the standard, with letters A through J assigned approximately in order of increasing cell volume, for cells typically manufactured at that time

https://en.wikipedia.org/wiki/Battery_nomenclature