A standard type one case 6-volt car battery goes into the K-F and Willys cars. If you have access to a Tractor Supply Store, their type 1 6-volt battery (at last check, anyway) featured the original type screw-off caps with threads in the walls of the filler holes; this will accept the correct diameter Sav-A-Battery filler caps. I had one in the 1952 Kaiser I had.