The AA battery (or double-A battery) is a standard size single cell cylindrical dry battery. ANSI and IEC battery nomenclature gives several designations for cells in this size, depending on cell features and chemistry. The IEC 60086 system calls the size R6, and ANSI C18 calls it 15. It is named UM-3 by JIS of Japan. Historically, it is known as D14 (hearing aid battery), U12 – later U7 (standard cell), or HP7 (for zinc chloride 'high power' version) in official documentation in the United Kingdom, or a pen cell.

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 (disposable) or a rechargeable battery. Several different chemistries are used in their construction. The exact terminal voltage, 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 (ANSI) in 1947, but it had been in use in torches (flashlights) and electrical novelties before formal standardization.

An AA cell measures 49.5–50.5 mm (1.95–1.99 in) in length, including the button terminal—and 13.7–14.5 mm (0.54–0.57 in) 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 and carry a maximum indent of 0.5 mm.

Alkaline AA cells have a weight of roughly 23 g (0.81 oz), lithium AA cells around 15 g (0.53 oz), and rechargeable Ni-MH cells around 31 g (1.1 oz).

Primary (non-rechargeable) zinc–carbon (dry cell) 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 which store around 1,000 to 1,500 mAh are often sold as "heavy duty" or "super heavy duty". Alkaline batteries from 1,700 mAh to 2,850 mAh cost more than zinc-chloride batteries, but hold additional charge. AA size alkaline batteries are termed as LR6 by IEC, and AM-3 by JIS.

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 a lithium iron disulfide battery with an open-circuit voltage below 1.7 volts is entirely discharged.

Rechargeable batteries in the AA size are available in multiple chemistries: nickel–cadmium (NiCd) with a capacity of roughly 600–1,000 mAh, nickel–metal hydride (NiMH) in various capacities of 600–2,750 mAh and lithium-ion. NiCd and NiMH provide 1.2 V; lithium-ion chemistry has a nominal voltage of 3.6–3.7 volts, and AA-sized cells of this voltage are coded 14500 rather than AA. AA-sized lithium-ion cells with circuitry to reduce the voltage to the 1.5V of standard replaceable cells are also made.