Coin Cell Batteries

Authors:

Geoffrey Hunter

Published On:

Sep 5, 2011

Last Updated:

May 30, 2026

Overview

Button cells are also known as coin cells or watch batteries.

Polarity

The insulated top cap of a button cell is the negative terminal, the base is the positive terminal.

Internal Resistance

The internal resistance of a coin cell battery is rather large. For example, a fresh CR2032 typically has an initial internal resistance of $\approx 10Ω$ . This then rapidly increases as the battery’s energy is consumed. Where high pulse currents are needed, coin cell batteries can be used in conjunction with high-valued capacitors.

A rule of thumb for coin cell batteries is that 10mA is the maximum current draw.

The internal resistance can be a better metric for the state-of-charge (SoC) than the cell voltage. Microcontrollers can measure this by:

Measuring the battery voltage with no load (or very little load)
Connecting a known large load and measuring the battery voltage again.
By looking at the voltage drop, the internal resistance can be calculated.
Use this to estimate the SoC.

Technologies

Silver Cell

Silver cells have a very stable output voltage over the lifespan of the battery.

Common Types

Most coin cells follow the IEC 60086 naming convention, where the part number encodes both the chemistry and the physical dimensions.¹ Taking the ubiquitous CR2032 as an example:

C: The chemistry. C denotes lithium manganese dioxide (LiMnO₂). Other common prefixes are B (lithium carbon monofluoride), L (alkaline manganese dioxide) and S (silver oxide).
R: The shape. R means round (cylindrical). There is also F for flat (layer built), P for prismatic and S for square (or rectangular or prismatic).¹
20: The diameter in millimetres (20mm).
32: The height in tenths of a millimetre (3.2mm).

So a CR2032 is a 20mm diameter, 3.2mm tall lithium cell, while a CR2025 is the same diameter but thinner at 2.5mm.

The first letter identifies the electrochemical system, which also implies a nominal voltage. The full set of IEC chemistry codes is given below (the negative electrode is referred to first):¹

Letter code	Negative electrode	Electrolyte	Positive electrode	Nominal voltage (V)	Max. open-circuit voltage (V)	Main article
(none)	Zinc	Ammonium chloride, Zinc chloride	Manganese dioxide	1.5	1.725	Zinc-carbon battery
A	Zinc	Ammonium chloride, Zinc chloride	Oxygen	1.4	1.55	Zinc-air battery
B	Lithium	Organic electrolyte	Carbon monofluoride	3.0	3.7	Lithium battery
C	Lithium	Organic electrolyte	Manganese dioxide	3.0	3.7
E	Lithium	Non-aqueous inorganic electrolyte	Thionyl chloride	3.6	3.9
F	Lithium	Organic electrolyte	Iron disulfide	1.5	1.83
G	Lithium	Organic electrolyte	Copper(II) oxide	1.5	2.3
L	Zinc	Alkali metal hydroxide	Manganese dioxide	1.5	1.65	Alkaline battery
M (withdrawn)	Zinc	Alkali metal hydroxide	Mercuric oxide	1.35		Mercury battery
N (withdrawn)	Zinc	Alkali metal hydroxide	Mercuric oxide, manganese dioxide	1.4
P	Zinc	Alkali metal hydroxide	Oxygen	1.4	1.68	Zinc-air battery
S	Zinc	Alkali metal hydroxide	Silver oxide	1.55	1.63	Silver-oxide battery
Z	Zinc	Alkali metal hydroxide	Manganese dioxide, nickel oxyhydroxide	1.5	1.78	Nickel oxyhydroxide battery

Lithium coin cells (CR/BR prefixes) have a nominal voltage of 3.0V, whereas silver oxide (SR) and alkaline (LR) cells are around 1.55V and 1.5V respectively. The table below lists some of the most common types:¹

Type	Chemistry	Diameter (mm)	Height (mm)	Nominal Voltage (V)	Typical Capacity (mAh)
CR1216	Lithium	12.5	1.6	3.0	25
CR1620	Lithium	16.0	2.0	3.0	75
CR1632	Lithium	16.0	3.2	3.0	120
CR2016	Lithium	20.0	1.6	3.0	90
CR2025	Lithium	20.0	2.5	3.0	165
CR2032	Lithium	20.0	3.2	3.0	225
CR2450	Lithium	24.5	5.0	3.0	620
LR44	Alkaline	11.6	5.4	1.5	110
SR44	Silver oxide	11.6	5.4	1.55	165

Note that the older alkaline (LR) and silver oxide (SR) “button” cells used in watches and small devices (e.g. LR44/SR44) do not follow the dimensional numbering scheme — their numbers are arbitrary type designators.

By far the most common coin cell in consumer electronics and on PCBs is the CR2032.

PCB Mounting

Coin cells are commonly used as backup batteries for real-time clocks (RTCs) on circuit boards. There are many PCB mount coin cell battery holders available on the market. This is a placeholder for the reference: fig-pcb-mount-cr1632-coin-cell-battery-holder shows a horizontal PCB mount CR1632 coin cell battery holder. You can also find vertical mount versions which don’t take up as much component area on the PCB at the expense of being taller.

A horizontal PCB mount CR1632 coin cell battery holder.

Dangers To Children

Coin cells are very dangerous to children if swallowed. They can cause severe internal burns due to the chemicals inside of them. Some coin cells have a bitter coating to help prevent children swallowing them, as shown in the below image:

A Duracell CR2032 button cell battery with a bitter coating to help prevent children swallowing them.

The Duracell coin batteries use non-toxic Bitrex (which is commonly used on other household products such as anti-nail biting solutions) as the bitter substance².

According to Duracell, the most dangerous sizes are:

2016
2025
2032

(i.e. all the button cells with a 20mm diameter)².

Some coin cells also have a dye added that colours a child’s mouth blue when ingested (to give you critical evidence you need to get them to the hospital fast).

In 2026, Energizer launched a new coin cell that was encased in a titanium alloy metal rather than the traditional stainless steel. This change prevents the burning that occurs in the digestive trap when a coin cell is swallowed.³ This arrived at the same time that Apple was facing a lot of criticism for their AirTag, which is a very compact device that uses a CR2032 and deemed a chocking and burn risk.⁴

Wikipedia (2025, Jul 17). Battery nomenclature [wiki]. Retrieved 2026-05-30, from https://en.wikipedia.org/wiki/Battery_nomenclature. ↩ ↩² ↩³ ↩⁴
Duracell. Duracell Power Safer - The only Lithium Coin Battery With Bitter Taste to Prevent Ingestion [website]. Retrieved 2024-04-28, from https://www.duracell-me.com/technology/lithium-coin-battery-safety/. ↩ ↩²
Yi-Jin Yu (2026, May 6). New battery aims to prevent some child deaths. Is it the solution?. ABC News. Retrieved 2026-05-30, from https://abcnews.com/GMA/Family/new-battery-aims-prevent-child-deaths-solution/story?id=132670770. ↩
Malcolm Owen (2026, May 6). Energizer’s Ultimate Child Shield batteries minimizes burns if your child swallows an AirTag battery. AppleInsider. Retrieved 2026-05-30, from https://appleinsider.com/articles/26/05/06/energizers-ultimate-child-shield-batteries-minimizes-burns-if-your-child-swallows-an-airtag-battery. ↩