The AA battery, also called a double A, penlite or Mignonbattery, is a standard sizesingle cell cylindrical dry battery. The IEC 60086 system calls it size R6, and ANSIC18 calls it size 15. It is named UM-3 by JIS of Japan. Historically, it is known as D14 or HP7 in official documentation in the United Kingdom. AA batteries are common in portable electronic devices. An AA battery is composed of a single electrochemical cell that may be either a primary battery or a rechargeable battery. Several different chemistries are used for their construction. The exact terminalvoltage, capacity and practical discharge rates depend on cell chemistry; however, devices designed for AA cells will usually only take 1.2-1.5 V unless specified by the manufacturer. Introduced in 1907 by The American Ever Ready Company, the AA battery size was standardized by the American National Standards Institute in 1947, but it had been in use in flashlights and electrical novelties before formal standardization. ANSI and IEC Battery nomenclature gives several designations for cells in this size, depending on cell features and chemistry. Due to their popularity in small flashlights, they are often called "penlight batteries".
Dimensions
An AA cell measures in length, including the button terminal—and in diameter. The positive terminal button should be a minimum 1 mm high and a maximum 5.5 mm in diameter, the flat negative terminal should be a minimum diameter of 7 mm. 14500 Lithium Batteries are longer if they feature a protection circuit up to 53 mm. Alkaline AA cells have a weight of roughly, lithium AA cells around, and rechargeable Ni-MH cells around.
Chemistry and capacity
Primary cells
Primary zinc–carbon AA batteries have around 400–900 milliampere hours capacity, with measured capacity highly dependent on test conditions, duty cycle, and cut-off voltage. Zinc–carbon batteries are usually marketed as "general purpose" batteries. Zinc-chloride batteries store around 1000 to 1500 mAh are often sold as "heavy duty" or "super heavy duty". Alkaline batteries from 1700 mAh to 2850 mAh cost more than zinc-chloride batteries, but hold additional charge. Non-rechargeable lithium iron disulfide batteries are manufactured for devices that draw more current, such as digital cameras, where their high cost is offset by longer running time between battery changes and more constant voltage during discharge. The capacity of alkaline batteries is greatly reduced as the discharge current increases, however the capacity of a Li-FeS2 battery is not affected by high discharge currents nearly as much as alkaline batteries. Another advantage of lithium disulfide batteries compared to alkaline batteries is that they are less prone to leak. This is particularly important in expensive equipment, where a leaking alkaline battery can damage the equipment due to the corrosive electrolyte coming into contact with sensitive electronics. Lithium iron disulfide batteries are intended for use in equipment compatible with alkaline zinc batteries. Lithium-iron disulfide batteries can have an open-circuit voltage as high as 1.8 volts but the closed-circuit voltage decreases, making this chemistry compatible with equipment intended for zinc-based batteries. A fresh alkaline zinc battery can have an open-circuit voltage of 1.6 volts, but an Lithium iron-disulfide battery with an open-circuit voltage below 1.7 volts is entirely discharged.
Rechargeable cells
Rechargeable batteries in the AA size are available in multiple chemistries: nickel–cadmium with a capacity of roughly 600–1000 mAh, nickel–metal hydride in various capacities of 600–2750 mAh and lithium-ion. Lithium ion chemistry has a nominal voltage of 3.6–3.7 volts, and are referred to as 14500 Li-ion batteries rather than AA. NiMH and Lithium Ion AA/14500 cells can supply most of their capacity even when under a high current drain, unlike Alkaline and Zinc-chloride cells which drop to a small fraction of their low current capacity before even reaching 1 C. A variant of the 14500 Li-ion batteries, sold by the Chinese company Kentli as "Kentli PH5" since 2014, comes with an internal buck converter at the positive electrode to downstep the output voltage from the normal 3.7 V to a very consistent 1.5 V AA standard voltage. It exposes the normal 3.7 V Li-ion electrode in a ring around the AA electrode for charging. Its more regular voltage provides better drop-in compatibility for alkaline AA devices, and its lithium-ion chemistry provides a lower self-discharge at 3% per month. It holds a mediocre capacity of 1600 mAh at 50 mA drain, limited by the low efficiency of the step-down converter. Nickel-zinc cell AAs are also available, but not widely used.
Comparison
Use
In 2011, AA cells accounted for approximately 60% of alkaline battery sales in the United States. In Japan, 58% of alkaline batteries sold were AA, known in that country as tansan. In Switzerland, AA batteries totaled 55% in both primary and secondary battery sales.
