Watch battery

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

A watch battery or button cell is a small form-factor battery designed for use in wrist watches, pocket calculators, hearing aids, and similar compact portable electronics products. Watch batteries are usually a single cell with nominal voltages 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 surface of these types of batteries is part of the positive (+) terminal.

1 Type designation
2 Other package markings
3 Common applications
4 Rechargeable variants
5 Other chemical compositions
6 References

[edit] Type designation

International standard IEC 60083-3 defines an alphanumeric coding system for watch batteries.

[edit] 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
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.

[edit] 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 diameter of the battery (downwards-rounded millimeters), and the last two digits indicate the overall height (downwards-rounded 0.1 millimeters). 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

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

32 = (3.20⁺⁰_−0.50) mm

[edit] 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.

[edit] 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).

[edit] Common applications

Quartz wrist watches, 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

[edit] Rechargeable variants

Regular watch batteries are not rechargeable. Rechargeable button cells are commercially available, but are not commonly used due to their inferior capacity.

[edit] 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).