A dead alkaline AA battery bounces, while a fresh one lands with a thud
Inside an alkaline AA cell, a zinc gel gradually turns into a ceramic as the battery is used. So a fresh cell dropped on a hard floor barely bounces, while a drained one springs back up. Princeton researchers even filmed the bounce height at every 10 percent of discharge.
The bounce test has limits. Because the change happens gradually and unevenly, a bounce does not prove a battery is empty, though a dead thud does show some charge remains. It is a quirk of one of the world's most familiar objects: in 2011, AA cells made up roughly 60 percent of alkaline battery sales in the United States and 58 percent in Japan, where the size is called tansan.
The format is older than most people guess. The American Ever Ready Company introduced it in 1907 for torches and electrical novelties, and the American National Standards Institute standardised it only in 1947. Official names vary widely: R6 under the international IEC system, 15 under ANSI, UM-3 in Japan, and historically U7 or HP7 in Britain, where it was also nicknamed a pen cell. A standard AA runs about 50 millimetres long and 14 millimetres wide, sitting between the smaller AAA and the larger C.
What is inside matters more than the shape. Cheap zinc–carbon cells hold roughly 400 to 900 milliampere-hours, heavy-duty zinc-chloride about 1,000 to 1,500, and alkaline between 1,700 and 2,850. Lithium iron disulfide cells cost more but suit power-hungry devices like digital cameras, hold their voltage steadier and are less likely to leak and damage equipment. Weight differs noticeably too, with lithium the lightest and nickel–metal hydride rechargeables the heaviest.
Rechargeables complicate the voltage picture. Nickel-based cells deliver 1.2 volts rather than the 1.5 volts of a fresh disposable, while lithium-ion cells the same size produce 3.6 to 3.7 volts and carry the code 14500 rather than AA. Since 2014 the Chinese firm Kentli has sold lithium-ion AAs with a built-in converter that steps output down to a steady 1.5 volts, and by 2023 several brands offered similar cells, some with a USB charging port built right into the battery.
Source: AA battery
