The B battery was what they used to call a radio battery and was something like 67 volts.   We've got an old grain moisture tester my dad had back in the 1960's that uses 2 of those things.  No longer available, but you can put a bunch of 9 volts together and come close enough to 130 volts DC that it could be used.

Getting back to the B battery, it was shaped about like a pack of cigarettes, only the battery was taller by about an inch and a half.