Competing brands of batteries can have substantially different dimensional specs. Where this dimensional tolerance has an impact is in the battery holder. A coin cell holder must be designed so it can handle normal height variances while at the same time, not accept batteries of a different type. Obviously, the battery holder can’t have a connection that’s too loose, because that would cause reliability issues. So if the user of the device can purchase replacement cells, the coin cell holder has to handle the full range of dimensions.
Script: A little known fact is that competing brands of batteries can have substantially different dimensional specs. Let’s look at a coin cell as an example. This device is a CR2032. It’s a button cell lithium battery rated at 3.0 volts. It is commonly used in computers as a CMOS battery, in remote controls, in watches, and in several other kinds of small devices.
The C in CR2032 indicates that this is a cell having a lithium negative electrode and a manganese dioxide positive electrode. The R indicates it has a round cylindrical form. The 20 in CR2032 indicates the cell has a 20 mm diameter and the 32 indicates a height of 3.2 mm as defined by the IEC standard 60086.
But according to ANSI and IEC standards a CR2032 coin cell can vary in height by ±0.3 mm. That doesn’t sound like much but it amounts to almost 10% of its total height. We’ve illustrated the dimensional tolerance on the side view of a typical CR2032. You can see that it is equivalent to the height of the lithium cathode.
Where this dimensional tolerance has an impact is in the battery holder. The coin cell holder has to be designed so it can handle normal height variances while at the same time, not accept batteries of a different type. Obviously, the battery holder can’t have a connection that’s too loose, because that would cause reliability issues. So if the user of the device can purchase replacement cells, the coin cell holder has to handle the full range of dimensions.
One last point about coin cell holders is that the soldering process also influences what kind of coin cell holder will work. For example, a coin cell holder that will be reflow soldered should be a high quality plastic such as a liquid crystal polymer so it can handle temperatures of at least 280°C. By contrast, battery holders that are wave soldered can be made of something less rugged materials such as PBT thermoplastic or nylon. These materials have a high dielectric strength and handle temperatures up to about 150 deg. C, 200 degrees with fiberglass reinforcement.