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A AA battery (IPA pronunciation: [eɪ eɪ] or [ˈdʌbl̩ eɪ]) is a dry cell-type battery commonly used in portable electronic devices. An AA battery measures 51mm in length (50.1mm without the button terminal), 13.5–14.5mm in diameter, and weighs approximately 23g (1.97×0.56 inches and 0.81 ounces).
As an AA battery is composed of a single chamber, it is more correctly referred to as a cell. Technically, a battery is a collection of cells working together, such as in a car battery. The more common term "battery" will be used throughout the rest of this article.
The nominal output voltage of single-use AA batteries is 1.5 volts, while rechargeable batteries have a nominal voltage of 1.2V. The voltage of a AA battery is the same as a AAA battery, C cell or D cell. AA batteries, however, provide power for a longer period than AAA batteries, because their larger size allows them to store more electrolyte. C and D cells, being larger still, can be expected to last longer again.
Primary (non-rechargeable) zinc-carbon AA batteries of 400–900 milliamp-hours capacity are common. Zinc-chloride batteries of 1000 to 1500 mAh are often sold as "long life" or "heavy duty". Alkaline batteries from 1700 mAh to almost 3000 mAh cost a little more, but last proportionally longer.
Single-use lithium AAs are also available for high demand devices such as digital cameras, where their high cost is offset by longer running time between battery changes. As of 2007, the only 1.5V lithium AA is manufactured by Eveready, although AA sized batteries with different nominal voltages are available from others. These should only be used in devices rated for the higher voltage.
The capacity of rechargeable AA batteries varies with the technology used. Nickel-cadmium (NiCd or NiCad) AAs with a capacity of 650 to 800 mAh are commonly available, while 800 to 1000 mAh AAs are rarer and more expensive. Nickel metal hydride (NiMH) AAs are also available in various capacities ranging from 1400 to 2900 mAh.
The older NiCd battery chemistry can supply a higher current than typical NiMHs, so NiCds are commonly used to power model cars or other relatively high-current-draw devices. New NiMH AAs designed for high current applications are beginning to become available. These use different construction and have lower capacity (1400–1600 mAh) than the highest capacity NiMH batteries.
Recently, AA-sized batteries have been introduced in rechargeable Li-ion chemistry. These batteries also do not supply voltage in the 1.2–1.5 V range and are thus not true AAs.
In September 2006 the USBCELL was launched with a built-in charger and USB connector within the AA format, enabling the battery to simply be charged by plugging into a USB port without external cables or adaptors.
The insides of a ZnC battery
The common zinc-carbon or zinc-chloride AA battery consists of a graphite or plastic rod in the center, paper, electrolytes, a zinc outer shell, and a plastic cover. There is also a pressure valve at the bottom to prevent explosions. However, the pressure valves generally will not prevent leakage or catastrophic failure of the shell if the battery is exposed to fire or extreme heat.
If a Zn-C or Zn-Cl battery is discharged too far then corrosion of the cathode, which is the zinc shell, can occur. If this becomes corroded enough, a breach in the shell can allow electrolyte to leak out. This is a common cause of damage to battery-powered appliances which are left unattended for long periods with batteries inside. The electrolyte can also cause minor skin damage, and should be kept away from eyes, and not ingested.
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Categories: Articles to be expanded since January 2007 | All articles to be expanded | Technology stubs | Battery shapes