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A watch battery, button cell, silver button cell, or coin cell is a small form-factor battery designed for use in wrist watches, pocket calculators, hearing aids, and similar compact portable electronics products. They are compact and have long life. Examples are mercury oxide and silver oxide cells. A mercury oxide cell has a mercury oxide cathode and a zinc anode. Watch batteries are usually a single cell with a nominal voltage between 1.5 and 3 V. Common anode materials are zinc or lithium; common cathode materials are manganese dioxide, silver oxide, carbon monofluoride or copper oxide. The cylindrical sides of these types of batteries is part of the positive (+) terminal.

Contents 1 Type designation 1.1 Electrochemical system 1.2 Package size 1.3 Final letters 2 Other package markings 3 Common applications 4 Rechargeable variants 5 Other chemical compositions 6 See also 7 References

Type designation

International standard IEC 60086-3 defines an alphanumeric coding system for watch batteries.

Electrochemical system

The first letter identifies the electrochemical system used in the battery, which also implies a nominal voltage:

Letter code	Positive electrode	Electrolyte	Negative electrode	Nominal voltage	End-point voltage
L	Manganese dioxide	Alkali	Zinc	1.5	1.0
S	Silver oxide	Alkali	Zinc	1.55	1.2
P	Oxygen	Alkali	Zinc	1.65	1.4
C	Manganese dioxide	Organic	Lithium	3	2.0
B	Carbon monofluoride	Organic	Lithium	3	2.0
G	Copper oxide	Organic	Lithium	1.5	1.2

The "C"-type 3-V lithium cells are today the most commonly-used type in quartz watches, calculators, small PDA devices, and computer motherboard clocks.

Package size

Its package's size is identified by a three-to-four digit code, preceded by the letter "R" to indicate a round cell. The first 1–2 digits indicate the outer breadth of the battery (in millimeters, rounded down), and the last two digits indicate the overall height (in tenths of millimeters, rounded down). Examples:

• CR2032: 20.0 mm diameter, 3.2 mm height
• SR516: 5.8 mm diameter, 1.6 mm height

ISO/IEC 83-3 lists the following diameter codes:

4 = 4.8⁺⁰_−0.15   mm

5 = 5.8⁺⁰_−0.15   mm

6 = 6.8⁺⁰_−0.15   mm

7 = 7.9⁺⁰_−0.15   mm

9 = 9.5⁺⁰_−0.15   mm

10 = 10.0⁺⁰_−0.20   mm

11 = 11.6⁺⁰_−0.20   mm

12 = 12.5⁺⁰_−0.25   mm

16 = 16⁺⁰_−0.25   mm

20 = 20⁺⁰_−0.25   mm

23 = 23⁺⁰_−0.50   mm

24 = 24.5⁺⁰_−0.50   mm

The following height codes are used with 16–24 mm diameter batteries:

12 = 1.20⁺⁰_−0.20   mm

16 = 1.60⁺⁰_−0.20   mm

20 = 2.00⁺⁰_−0.25   mm

25 = 2.50⁺⁰_−0.50   mm

30 = 3.00⁺⁰_−0.50   mm

36 = 3.60⁺⁰_−0.50   mm

50 = 5.00⁺⁰_−0.50   mm

Final letters

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

• S: sodium hydroxide electrolyte
• P: potassium hydroxide electrolyte
• no letter: organic electrolyte

An appended letter "W" states that this battery complies with all the requirements of the IEC 86-3 standard for watch batteries.

Other package markings

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.

The manufacturing date can be abbreviated to the last digit of the year, followed 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).

Common applications

• Quartz wristwatches, both digital and analog.
• Calculators
• Hearing aids
• Some remote controls, especially for keyless entry
• Backup power for personal computer real time clocks and BIOS configuration data.
• Small PDA devices
• Various electronic toys (tamagotchi)
• Laser pointers
• Small LED flashlights are commonly powered by three button (silver-oxide) cells in series.
• Battery-operated children's books
• Glucometers
• Security tokens
• Cyclocomputers
• Red dot sights and electronic spotting scopes

Rechargeable variants

Regular watch batteries are not rechargeable. Rechargeable button cells are commercially available, but are not commonly used due to their inferior capacity or higher self-discharge. Also, watch batteries are usually used in low-power devices where batteries are replaced very rarely so there is no big benefit from using rechargeable batteries but higher self-discharge rate and lower capacity could make using rechargeable batteries impractical. As of 2008 there are some commercially-available rechargeable watch batteries, usually intended to replace CR lithium batteries in devices with relatively high current consumption.

Other chemical compositions

• Mercury cells are now banned from sale in many countries.
• Alkali cells are sometimes found in low-end markets, but do only provide a fraction of the capacity of silver oxide or lithium based cells.
• Zinc-air cells utilize air in the chemical reaction. (It is required to remove a plastic foil layer before usage.)

See also

• Battery recycling
• Battery Equivalents: Consumer and Specialist Types
• Laminar battery

References

• http://howtochangeawatchbattery.com
• IEC 60086-3: Primary batteries — Part 3: Watch batteries. International Electrotechnical Commission, Geneva, 1995. (also: BS EN 60086-3:1996)
• An Investigation of Alternatives to Miniature Batteries Containing MercuryPDF (440 KiB)
• Battery Reference chart. Renata Watch Batteries

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Wikipedia content modification information:

• This page was last modified on 2 January 2009, at 20:45.

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