Button cell

The first letter in the IEC standard system identifies the chemical composition of the battery, which also implies a nominal voltage:

For types with stable voltage falling precipitously at end-of-life (cliff-top voltage-versus-time graph), the end-voltage is the value at the "cliff-edge", after which the voltage drops extremely rapidly. For types which lose voltage gradually (slope graph, no cliff-edge) 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 (oxide) 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 (cylindrical) 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.

Several sizes of button and coin cell with four 9 V batteries as a size comparison

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.

Examples:

• CR2032: lithium, 20 mm diameter, 3.2 mm height, 220 mAh
• CR2032H; lithium, 20 mm diameter, 3.2 mm height 240 mAh
• CR2025: lithium, 20 mm diameter, 2.5 mm height, 170 mAh
• SR516: silver, 5.8 mm diameter, 1.6 mm height
• LR1154/SR1154: alkaline/silver, 11.6 mm diameter, 5.4 mm height. The two-digit codes LR44/SR44 are often used for this size

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.[7]

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

• P: potassium hydroxide electrolyte
• S: sodium hydroxide electrolyte
• No letter: organic electrolyte
• SW: low drain type for quartz watches (analog or digital) without light, alarm, or chronograph functions
• W: high drain type for all quartz watches, calculators and cameras. The battery complies with all the requirements of the international IEC 60086-3[8] standard for watch batteries.

Type CR2032 watch battery (lithium anode, 3 V, 20.0 mm × 3.2 mm)

Leaked and corroded button cell

Apart from the type code described in the preceding section, watch batteries should also be marked with

• the name or trademark of the manufacturer or supplier;
• the polarity (+);
• the date of manufacturing.

Often a 2-letter code (sometimes on the side of the battery) where the first letter identifies the manufacturer and the second is the year of manufacture. For example:

• YN – the letter N is the 14th letter in the alphabet – indicates the cell was manufactured in 2014.

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 (e.g., 01 = January 1990 or January 2000, 9Y = November 1999 or November 2009).

A code used by some manufacturers is AG (alkaline) or SG (silver) followed by a number, as follows

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

Coin cells being tested

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.[10]

Swallowed batteries can cause damage to the lining of the oesophagus, and can create a hole in the oesophagus lining in two hours.[10] 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.[10]

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.[11] Coin cells of diameter 20 mm or greater cause the most serious injuries, even if expended and intact.[11][12] In Auckland, New Zealand as of 2018 there are about 20 cases per year requiring hospitalization.[13]

In 2020, Duracell announced that they were coating some of their lithium button cells with a bitterant compound to discourage children from ingesting them.[14]

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.[15][16]

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.[11][12] Such impactions can rapidly devolve and cause severe tissue injury in as little as two hours.[12][17][18] The damage is not caused by the contents of the battery, but by the electric current that is created when the anode (negative) 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 (caustic soda) build-up near the battery's anode face (cathodic reaction in the electrolyte). This results in the liquefactive necrosis of the tissue, a process whereby the tissue effectively is melted away by the alkaline solution.[17] 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.[18] As a result of these findings, US-based National Capital Poison Center (Poison Control) 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.[19] 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.[20][21] 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".[1]