Nippon Kogaku manufactured a small Bakelite battery tester sometimes known as a volt meter for the Nikon rangefinder S-36 motor drives. This has a measuring range of up to 11 V, whereas the battery tester for the Nikon F-36 motor drive measures up to 14 V.
The battery tester can be applied to the socket of the separate battery pack in order to see if the charge is sufficient to power more rolls of film through the camera. If the needle is well over the middle of the scale, the batteries have sufficient charge. The tester first appeared in the price list of August 1960 and was offered until the late 1960s when the Cordless Battery Pack was introduced which did not provide a terminal to test the batteries.
*This is the battery tester for the Nikon F