Q: There are AAA, AA, C and D batteries. What happened to sizes A and B?
A: The AA, C and D size designations originated in the US at a time when battery-operated valve radio receivers were used widely. These receivers had already laid claim to the A and B designations: the A battery (usually a lead-acid accumulator) heated the filaments of the valves, while the B-battery provided the highvoltage supply for the anodes. Therefore, new cells could not use the same names and the AA, C and D sizes had to be adopted.
One can still see 鈥淏 supply鈥� or B+ on present-day circuit diagrams and the term C battery was also used, for the grid-bias supply, but it may be that the new C cell designation was adopted before grid-bias batteries came into use.
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Another explanation sometimes offered is that A and B cells were used only in multicell batteries and never marketed as single cells.
In Britain, individual battery manufacturers had, and to some extent still have, their own type designations, such as PP3 and 996 and even No. 8, which was used widely in the Second World War.
The AAA and other new sizes such as N, are now standardised internationally according to IEC86, a two-part standard published by the International Electrotechnical Commission in Geneva.
The equivalent British Standard is B5397, the third part of which includes cell sizes used only in Britain.