Coin Cell Batteries

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 starts of at a rather large 10Ω. This then rapidly increases as the batteries 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.

Technologies

Silver Cell

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

Common Types

CR2032. CR2025.

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:

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 substance¹.

According to Duracell, the most dangerous sizes are:

• 2016
• 2025
• 2032

(i.e. all the button cells with a 20mm diameter)¹.

References