The Feldfernsprecher 33, Ortsbatterie Betrieb 43, and Tischfernsprecher 38 field telephones were designed to operate with a 1.5 volt cell powering the microphones in the handsets. The reason why 1.5 volts was selected was to increase the service life of the carbon microphone capsules.
During wartime, the aforementioned field telephones were powered by a T30 which was a 1.5 volt air activated dry cell. This cell was rectangular in shape and had a paper label. They were manufactured by numerous firms including Hermann Albert Bumke, Koch & Krüger, Pertrix, Carbone, Hamburger Batterie Fabrik (HABAFA), and Hugo Falk. The labels all included the code “ELL.”
What does the ELL code mean? Well, the first letter, “E,” stands for “element,” which is the German word for cell. The second letter, “L,” corresponds to the cell size, which is 55 x 55 x 125 mm. The third letter “L,” stands for the type of cell. In this case, Luftsauerstoffelement, or air activated cell.
For more information about field telephone T30 cells, refer to my WW2 German field telephone equipment book…
WW2 German Field Telephone Equipment 