nicad-battery

Ads

AA battery

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-cadium), HR6 (nickel-metal-hydride), and FR6 (lithium-iron-disulfide). Other names include MN1500 and HP7. In France it's known colloquially as Mignon. An AA battery is composed of a single electrochemical cell.

Dimensions

An 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 an 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 milli amp-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 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 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 650 to 800 mAh are commonly available, while 800 to 1100 mAh AA types are rarer and more expensive. Nickel-metal hydride (NiMH) AAs are also available in various capacities ranging from 1300 to 2900 mAh.

AA rechargeable batteries supply 1.2 Volts, and as such, there can be problems powering some devices. For instance, a device powered by 4 AA batteries uses 6 Volts, but when powered from rechargebles the voltage will be 4.8 V, which may not be in the normal operating range. Some devices include warnings not to be used with rechargeable batteries.

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. A newer form, low self-discharge NiMH batteries, are sold precharged 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.

The insides of a ZnC battery

The 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, 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, 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.

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.