BTW, your question brings up an interesting point.
You slightly mislead us by talking about battery sizes (defined by NEDA?)
A, B, C, D, and AA and AAA
But in the old days, the usage designations were widely used A was for
filament, B for plate supply and C for tube bias. If your tube plates needed 90
volts, the grids might need 45.
You used C batteries because to drop the voltage from a B battery was very
wasteful (resistor heat), and batteries were expensive.
The B batteries were almost always square or box-like, and C and A could be any
shape. The D cells were used for illumination (dial lights and the like).
Batteries could be designed for high current, low voltage, or low current high
voltage, or some variation thereof to suit the purpose.
Even today, if you go into Radio Shack and get the l;ittle coin-sized
batterries used in calculators and the like, you'll have several different
versions of the same shape.
Some have their internal chemistry optimized for low current, long life
(digital clock or memory battery backup in a PC), while others are designed for
infrequent bursts of high current draw (garage door openers). That is why if
you're in a bind, you can probably substitute another battery number for one
that's not in stock, but it won't last as long because it won't be optimized
for the job. But the size has to be the same, of course.
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