what’s the difference between AA and AAA and other batteries? Why do we have a bunch of different ones?
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In the days before transistors, there were portable radios that used vacuum tubes. These required two kinds of batteries.
1. A low voltage battery to heat the filaments of the tubes. This was called the A battery.
2. A high voltage battery to supply the plate voltage for the tubes. This was called the B battery.
Later when letters were used for different battery sizes, B was not used for a low voltage battery size, since it was already used for the high voltage plate battery.
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