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AA battery
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A AA battery ( or ) is a dry cell-type battery commonly used in portable electronic devices. The AA battery type was standardized by ANSI in 1947, and is designated E91 by DIN and AM3 by JIS. Internationally the IEC designated it as LR6 (alkaline), R6 (carbon-zinc), KR157/51 (nickel-cadmium), HR6 (nickel-metal-hydride), and FR6 (lithium-iron-disulfide).
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A AA battery ( or ) is a dry cell-type battery commonly used in portable electronic devices. The AA battery type was standardized by ANSI in 1947, and is designated E91 by DIN and AM3 by JIS. Internationally the IEC designated it as LR6 (alkaline), R6 (carbon-zinc), KR157/51 (nickel-cadmium), HR6 (nickel-metal-hydride), and FR6 (lithium-iron-disulfide). Other names include MN1500 and HP7. In China it is known as the #5 battery. In Germany it is known colloquially as Mignon. An AA battery is composed of a single electrochemical cell.
Dimensions
AA battery measures 51 mm in length (50.1 mm without the button terminal), 13.5–14.5 mm in diameter, (1.97×0.56 inches). Traditional alkaline AA batteries have mass of roughly 23 g (0.81 ounces), Lithium AA batteries have mass around 15 g (0.5 oz), and rechargeable NiMH batteries have mass about 31 g (1.1 oz).
Inner Workings
The nominal output voltage of single-use AA batteries is 1.5 volts, while NiCd and NiMH rechargeable batteries have a nominal voltage of 1.2 V. Specialty batteries based on more unusual chemistries can run at a voltage as high as 1.6 V under load. 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 a greater mass of anode material which is consumed as it does electrical work. C and D cells, being larger, last longer still; as a rough guide, the capacity of a battery scales linearly with its mass.
Primary (non-rechargeable) zinc-carbon AA batteries of 400–900 milliamp-hours capacity are commonly made using Leclanché cell technology. 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 (ie. non-rechargeable) lithium batteries 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 2008, the only 1.5 V lithium AA called "Ultimate Lithium" is manufactured by Energizer, although AA-sized batteries with different nominal voltages are available from others. These should only be used in devices rated for the higher voltage.
Rechargeable AA batteries
The capacity of rechargeable AA batteries varies with the technology used. Nickel-cadmium (NiCd or NiCad) AAs with a capacity of 500 to 1100 mAh are available, cost increasing with capacity. Nickel-metal hydride (NiMH) AAs are also available in various capacities ranging from 1300 to 2900 mAh.
AA rechargeable batteries supply 1.2 V; since this is lower than the voltage of standard non-rechargeable cells, there are problems powering some devices with these batteries. For example, a device designed may be designed to use 4 alkaline AA batteries in series, producing 6 V, and may fail to operate satisfactorily with the reduced voltage of 4.8 V produced by 4 NiMH AA batteries. Some devices include warnings specifically indicating against use with rechargeable batteries, while many newer electronic devices are specifically designed to tolerate the lower voltage.
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 (typically 1400–1600 mAh) than the highest capacity NiMH batteries (above 2000 mAh).
Rechargeable AA batteries suffer from self discharge, whereby a full battery loses its charge when stored for a significant period of time. This effect is quite severe for NiMH batteries, which may lose 20% of full charge after 60 days of storage. A newer form, the low self-discharge NiMH battery, is distinguished by a much lower rate of discharge, claimed to be around 8% after 60 days . These batteries can be sold pre-charged and ready for use.
Rechargeable AA-sized batteries based on Li-ion chemistry have also been introduced. These batteries do not supply voltage in the 1.2–1.5 V range and are thus not compatible with most AA-based devices.
Inside a ZnC battery
The formerly common zinc-carbon or zinc-chloride AA battery consists of a graphite rod in the center forming an electrode, an anode/electrolyte mix consisting mainly of manganese oxide, a zinc outer shell which serves as the cathode, and a paper, plastic or steel cover. See Zinc-carbon battery. There is sometimes a pressure valve at the bottom to prevent explosions. However, this 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, corrosion of the cathode, which is the zinc shell, can occur. If it 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.
Inside an alkaline battery
More common today than the lower cost ZnC batteries are alkaline cells. Different variants exist, offering roughly two to three times the capacity of ZnC cells. Rather than zinc chloride as the electrolyte, potassium hydroxide is used.
See also
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