Coin cell tips

[mklotz]

Button/Coin cells/batteries are common in many of the electronic devices we use. I collected some information about them and pass it along here along with a couple of tips that might be useful when working with them.

First, you should read the excellent Wikipedia article on the subject...

https://en.wikipedia.org/wiki/Button_cell

in which you will find this chart...



that helps to explain the information contained in the designation printed on the battery.

Another chart from that article...



is also very useful for determining size.

For example, from the two charts we can deduce that the common CR2032 has the following properties:

C = lithium with a nominal voltage of 3.0 volts
R = round (cylindrical) form [this is discussed in the article]
20 = 20 mm diameter
32 = 3.2 mm thickness

while an LR44 (another common battery)

L = alkaline with a nominal voltage of 1.5 volts
R = round
44 = 11.6 mm diameter [apparently some inferial luddite snuck in during the chart's creation]

The proper designation should be LR1154.

There's not much use for plastic calipers in a machine shop but they do have the advantage of being non-conductive which makes them ideal for measuring batteries and other devices one wouldn't want to short. I suppose steel calipers could have their jaws insulated with painter's tape or such then, if electronic, simply close them and rezero.

I've never encountered a specification for testing these batteries under load. I just test them by measuring their unloaded voltage with a VOM. The "End Point Voltage" shown in the first chart is a good breakpoint for deciding between good and bad. For coarser work I just use half their nominal voltage.

Measuring voltage with the VOM can be done by laying the battery positive side down and holding it by pinning it with the negative lead. Then the positive lead must be carefully slid against the side of the battery. This procedure can get tricky and risks shorting the battery. I prefer to lay the battery negative side down on a small copper plate (or a clean coin of diameter larger than the battery) and apply the negative lead to the plate and the positive to the battery.

Conventional tweezers can't be used to manipulate these batteries for obvious reason; they would short the terminals. One can buy rubber-tipped tweezers...

https://www.amazon.com/Tweezers-twee...s%2C161&sr=8-1

or dip the tips of conventional tweezers in the liquid insulation used by electricians.