When were AA batteries first introduced?

An AA battery is a standard size single cell cylindrical dry battery; the IEC system calls it size R6, and ANSI calls it size 15. They are common in portable electronic devices. An AA battery is composed of a single electrochemical cell that may be either a primary battery (disposable) or a rechargeable battery. The exact terminal voltage and capacity of an AA size battery depend on cell chemistry.

Introduced in 1907, the AA battery size was finally standardized by the American National Standards Institute (ANSI) in 1947, but it had been used in flashlights and electrical novelties before formal standardization.