What does each ‘A’ in AAA & AA battery stand for? What’s the basis for the common names of batteries.

Contributor | OK, some of the answers below provide the “why” for the multiple letters, but a bit of history will clarify the use of letters for batteries. In the early days of radio, the vacuum tube was king. And rectification of ac was crude and used a selenium rectifier to provide the DC voltages to allow vacuum tubes to operate. Making a radio portable was a whole new ball game and to allow that, they manufactured special batteries to perform specific tasks in a portable tube radio. A low volt ; high current battery drove the filament. A high voltage; low current battery drove the plate circuit. There was a third mid-level battery to power the grid with almost zero current draw within a radio. At the time, a schematic used multiple notations to define these different power sources. They were noted by A+ (filament battery), B+ (plate battery) and C+ (grid bias battery) voltage potentials on the schematics. Therefore, the batteries supplying those power sources were named A, B, and C by the battery manufacturers. If you note in many schematics found today in hobby and industry schematics, one of those notations is still in use today, “B+”. In old days, that was the plate power for the radio’s tubes, so it was considered the main supply voltage of the circuit. As the transistor took over, most of these odd shaped and rated batteries became obsolete. The lettering system stayed around. The letter system is based in the US, the rest of the world uses a number system for these batteries, with the UK and a few other countries being an exception.