AA Battery
Direct Answer
A standard AA battery measures 14.5mm in diameter and 50.5mm in length. Primary Alkaline cells output 1.5V, NiMH rechargeable cells output 1.2V. Inserting a 3.6V 14500 Li-ion cell into 1.5V AA devices destroys the circuit.
Source: IEC 60086-2
Specs
| Diameter | 14.50 mm |
| Length | 50.50 mm |
| Alkaline Voltage | 1.50 V |
History & Origin
The AA cell was introduced in 1907 by the American Ever Ready Company, though it circulated for decades afterward under earlier trade names before the AA label became standard. It wasn't until 1947 that the American National Standards Institute formally standardized the AA size, which is what allowed batteries from competing manufacturers to become fully interchangeable in the same devices -- the AAA size followed with its own ANSI standard in 1959.
Today the AA format spans multiple chemistries under different IEC codes: LR6 for alkaline (1.5V), FR6 for lithium (1.5V), and R6 for the older zinc-carbon cells, alongside HR6 for NiMH rechargeables at 1.2V nominal -- all sharing the same physical dimensions.
The 14500 Substitution Risk
The 14500 lithium-ion cell is built to the same physical dimensions as an AA cell but runs at roughly 3.6-3.7V nominal -- more than double a standard AA's 1.5V. Because it fits mechanically into any AA-sized battery holder, it's an easy mistake to make, but the overvoltage can destroy circuitry designed around 1.5V logic, and many AA-only devices have no protection against reversed polarity or overvoltage since alkaline and NiMH cells never posed that risk. The safe rule is to match voltage and chemistry, not just physical size, when choosing a replacement cell.