C, and D as sizes increased. But as batteries got smaller, ANSI ran out of letters. Instead of starting over, they doubled down — literally. That's how we ended up with AA, AAA, and even AAAA.

Please note that the most common type of battery, the alkaline, in the form of C, D, AA, AAA, and 9 volt, is not considered hazardous. Alkaline batteries may be discarded in the trash. Most batteries ...