Button cell


A watch battery or button cell is a small single cell battery shaped as a squat cylinder typically in diameter and high — resembling a button. A metal can forms the bottom body and positive terminal of the cell. An insulated top cap is the negative terminal.
Button cells are used to power small portable electronics devices such as wrist watches, and pocket calculators. Wider variants are usually called coin cells. Devices using button cells are usually designed around a cell giving a long service life, typically well over a year in continuous use in a wristwatch. Most button cells have low self-discharge and hold their charge for a long time if not used. Relatively high-power devices such as hearing aids may use a zinc–air battery which have much higher capacity for a given size, but dry out after a few weeks even if not used.
Button cells are single cells, usually disposable primary cells. Common anode materials are zinc or lithium. Common cathode materials are manganese dioxide, silver oxide, carbon monofluoride, cupric oxide or oxygen from the air. Mercuric oxide button cells were formerly common, but are no longer available due to the toxicity and environmental effects of mercury.
Cells of different chemical composition made in the same size are mechanically interchangeable. However, the composition can affect service life and voltage stability. Using the wrong cell may lead to short life or improper operation. Sometimes different cells of the same type and size and specified capacity in milliampere-hour are optimised for different loads by using different electrolytes, so that one may have longer service life than the other if supplying a relatively high current.
Button cells are very dangerous for small children. Button cells that are swallowed can cause severe internal burns and significant injury or death.

Properties of cell chemistries

are made in the same button sizes as the other types, but typically provide less capacity and less stable voltage than more costly silver oxide or lithium cells.
Silver cells may have a stable output voltage until it suddenly drops at end of life. This varies for individual types; one manufacturer offers three silver oxide cells of the same size, 357-303, 357-303H and EPX76, with capacities ranging from 150 to 200 mAh, voltage characteristics ranging from gradually reducing to fairly constant, and some stated to be for continuous low drain with high pulse on demand, others for photo use.
Mercury batteries also supply a stable voltage, but are now banned in many countries due to their toxicity and environmental impact.
Zinc-air batteries use air as the depolarizer and have much higher capacity than other types, as they take that air from the atmosphere. Cells have an air-tight seal which must be removed before use; they will then dry out in a few weeks, regardless of use.
For comparison, the properties of some cells from one manufacturer with diameter 11.6 mm and height 5.4 mm were listed in 2009 as:
Examining datasheets for a manufacturer's range may show a high-capacity alkaline cell with a capacity as high as one of the lower-capacity silver types; or a particular silver cell with twice the capacity of a particular alkaline cell. If the powered equipment requires a relatively high voltage to operate correctly, a silver cell with a flat discharge characteristic will give much longer service than an alkaline cell—even if it has the same specified capacity in mAh to an end-point of 0.9 V. If a device seems to "eat up" batteries after the original supplied by the manufacturer is replaced, it may be useful to check the device's requirements and the replacement battery's characteristics. For digital calipers, in particular, some are specified to require at least 1.25 V to operate and others 1.38 V.
While alkaline, silver oxide, and mercury batteries of the same size may be mechanically interchangeable in any given device, use of a cell of the right voltage but unsuitable characteristics can lead to short battery life or failure to operate equipment. Common lithium primary cells, with a terminal voltage around 3 volts, are not made in sizes interchangeable with 1.5 volt cells. Use of a battery of significantly higher voltage than equipment is designed for can cause permanent damage.

Type designation

60086-3 defines an alphanumeric coding system for "Watch batteries". Manufacturers often have their own naming system; for example, the cell called LR1154 by the IEC standard is named AG13, LR44, 357, A76, and other names by different manufacturers. The IEC standard and some others encode the case size so that the numeric part of the code is uniquely determined by the case size; other codes do not encode size directly.
Examples of batteries conforming to the IEC standard are CR2032, SR516, and LR1154, where the letters and numbers indicate the following characteristics.

Electrochemical system

The first letter in the IEC standard system identifies the chemical composition of the battery, which also implies a nominal voltage:
Letter
code		Common
name		Positive
electrode		ElectrolyteNegative
electrode		Nominal
voltage 		End-point
voltage
LAlkalineManganese dioxideAlkaliZinc1.51.0
SSilverSilver oxideAlkaliZinc1.551.2
PZinc-airOxygenAlkaliZinc1.41.2
CLithiumManganese dioxideOrganicLithium32.0
BCarbon monofluorideOrganicLithium32.0
GCopper oxideOrganicLithium1.51.2
ZNickel oxyhydroxideManganese dioxide, nickel oxyhydroxideAlkaliZinc1.5?
M, N MercuryMercuric oxideAlkaliZinc1.35/1.401.1

For types with stable voltage falling precipitously at end-of-life, the end-voltage is the value at the "cliff-edge", after which the voltage drops extremely rapidly. For types which lose voltage gradually the end-point is the voltage beyond which further discharge will cause damage to either the battery or the device it is powering, typically 1.0 or 0.9 V.
Common names are conventional rather than uniquely descriptive; for example, a silver cell has an alkaline electrolyte.
L, S, and C type cells are today the most commonly used types in quartz watches, calculators, small PDA devices, computer clocks, and blinky lights. Miniature zinc-air batteries – P type – are used in hearing aids and medical instruments. In the IEC system, larger cells may have no prefix for the chemical system, indicating they are zinc-carbon batteries; such types are not available in button cell format.
The second letter, R, indicates a round form.
The standard only describes primary batteries. Rechargeable types made in the same case size will carry a different prefix not given in the IEC standard, for example some ML and LiR button cells use rechargeable lithium technology.

Package size

Package size of button batteries using standard names is indicated by a 2-digit code representing a standard case size, or a 3- or 4-digit code representing the cell diameter and height. The first one or two digits encode the outer diameter of the battery in whole millimeters, rounded down; exact diameters are specified by the standard, and there is no ambiguity; e.g., any cell with an initial 9 is 9.5 mm in diameter, no other value between 9.0 and 9.9 is used. The last two digits are the overall height in tenths of a millimeter.
Number
code		Nominal
diameter 		Tolerance
44.8±0.15
55.8±0.15
66.8±0.15
77.9±0.15
99.5±0.15
1010.0±0.20
1111.6±0.20
1212.5±0.25
1616.0±0.25
2020.0±0.25
2323.0±0.50
2424.5±0.50
445.4±0.20

Examples:
Some coin cells, particularly lithium, are made with solder tabs for permanent installation, such as to power memory for configuration information of a device. The complete nomenclature will have prefixes and suffixes to indicate special terminal arrangements. For example, there is a plug-in and a solder-in CR2032, a plug-in and three solder-in BR2330s in addition to CR2330s, and many rechargeables in 2032, 2330, and other sizes.

Letter suffix

After the package code, the following additional letters may optionally appear in the type designation to indicate the electrolyte used:

Other package markings

Apart from the type code described in the preceding section, watch batteries should also be marked with
Often a 2-letter code where the first letter identifies the manufacturer and the second is the year of manufacture. For example:
There is no universal standard.
The manufacturing date can be abbreviated to the last digit of the year, followed by a digit or letter indicating the month, where O, Y, and Z are used for October, November and December, respectively.

Common manufacturer code

A code used by some manufacturers is AG or SG followed by a number, as follows
G codeIEC code
xG0521
xG1621
xG2726
xG3736
xG4626
xG5754
xG6920 or 921
xG7926 or 927
xG81120 or 1121
xG9936
xG101130 or 1131
xG11721
xG121142
xG131154

To those familiar with the chemical symbol for silver, Ag, this may suggest incorrectly that AG cells are silver.

Common applications

Rechargeable variants

In addition to disposable button cells, rechargeable batteries in many of the same sizes are available, with lower capacity than disposable cells. Disposable and rechargeable batteries are manufactured to fit into a holder or with solder tags for permanent connection. In equipment with a battery holder, disposable or rechargeable batteries may be used, if the voltage is compatible.
A typical use for a small rechargeable battery is to back up the settings of equipment which is normally permanently mains-powered, in the case of power failure. For example, many central heating controllers store operation times and similar information in volatile memory, lost in the case of power failure. It is usual for such systems to include a backup battery, either a disposable in a holder or a soldered-in rechargeable.
Rechargeable NiCd button cells were often components of the backup battery of older computers; non-rechargeable lithium button cells with a lifetime of several years are used in later equipment.
Rechargeable batteries typically have the same dimension-based numeric code with different letters; thus CR2032 is a disposable battery while ML2032, VL2032 and LIR2032 are rechargeables that fit in the same holder if not fitted with solder tags. It is mechanically possible, though hazardous, to fit a disposable battery in a holder intended for a rechargeable; holders are fitted in parts of equipment only accessible by service personnel in such cases.

Health issues

Accidental ingestion

Button cells are attractive to small children; they may put them in their mouth and swallow them. The ingested battery can cause significant damage to internal organs. The battery reacts with bodily fluids, such as mucus or saliva, creating a circuit which can release an alkali that is strong enough to burn through human tissue.
Swallowed batteries can cause damage to the lining of the oesophagus, and can create a hole in the oesophagus lining in two hours. In severe cases, damage can cause a passage between the oesophagus and the trachea. Swallowed button cells can damage the vocal cords. They can even burn through the blood vessels in the chest area, including the aorta.
In Greater Manchester, England, with a population of 2,700,000, two children between 12 months and six years old died, and five suffered life-changing injuries, in the 18 months leading up to October 2014. In the United States, on average over 3,000 pediatric button batteries ingestions are reported each year with a trend toward major and fatal outcomes increasing. Coin cells of diameter 20 mm or greater cause the most serious injuries, even if expended and intact. In Auckland, New Zealand as of 2018 there are about 20 cases per year requiring hospitalization.

Mercury and cadmium

Some button cells contain mercury or cadmium, which are toxic. In early 2013 the European Parliament Environment Committee voted for a ban on the export and import of a range of mercury-containing products such as button cells and other batteries, to be imposed from 2020.

Lithium

Lithium cells, if ingested, are highly dangerous. In the pediatric population, of particular concern is the potential for one of these batteries to get stuck in the oesophagus. Such impactions can rapidly devolve and cause severe tissue injury in as little as two hours. The damage is not caused by the contents of the battery, but by the electric current that is created when the anode face of the battery comes in contact with the electrolyte-rich esophageal tissue. The surrounding water undergoes a hydrolysis reaction that produces a sodium hydroxide build-up near the battery's anode face. This results in the liquefactive necrosis of the tissue, a process whereby the tissue effectively is melted away by the alkaline solution. Severe complications can occur, such as erosion into nearby structures like the trachea or major blood vessels, the latter of which can cause fatal bleeds.
While the only cure for an esophageal impaction is endoscopic removal, a 2018 study from Children's Hospital of Philadelphia by Rachel R. Anfang and colleagues found that early and frequent ingestion of honey or sucralfate suspension prior to removal can reduce the injury severity to a significant degree. As a result of these findings, US-based National Capital Poison Center updated its triage and treatment guideline for button battery ingestions to include the administration of honey and/or sucralfate as soon as possible after a known or suspected ingestion. Prevention efforts in the US by the National Button Battery Task force in cooperation with industry leaders have led to changes in packaging and battery compartment design in electronic devices to reduce a child's access to these batteries. However, there still is a lack of awareness across the general population and medical community to its dangers. Central Manchester University Hospital Trust warns that "a lot of doctors are unaware that this can cause harm".