When I was working out on Superior, the guys from WHOI (Woods-Hole Oceanographic Institute or something) used F-cell batteries in their data loggers. Same diameter as D-cells, but 1.5-2x longer. They had a contract directly with the manufacturer in order to keep getting them - I believe they were the only ones using them. Since they were special order, and not commercial products, there were no labels on the batteries. Just the plain metal casing.