Regarding the "B battery":
Before there were "chips", or even transistors, there were devices called vaccuum tubes which performed the same functions. In order to operate, tubes required two voltages: a low voltage to operate the "filament", or "heater", which generated heat necessary for the tube to operate, and a high voltage which actually did the work.
The low voltage battery in portable radios was called the "A" battery. The high voltage battery was called the "B" battery.
You can't find B batteries anymore because there is no need for them. So
there you have it!
Please refer to this site for more info (http://www.angelfire.com/ma2/AdamVon/tobatt.html
), I would really not like to type the whole thing out. The gist is that A and B sized were used in old antique radios. They do exist and are still made by Eveready in 22.5, 45 and 67.5 volt batteries.