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Ever Wonder About Button Batteries?

I needed a new battery for the little light that I clip to my dog’s leash when I take her for walks at night. It was a small round metal battery, so small that my middle-aged eyes couldn’t make out the inscription. I took it to my local hardware store and they thought they found the right one, but it didn’t work—turns out it was about the same size, but the wrong voltage. They didn’t carry the one I needed. I took a picture of it (with a sunflower seed for scale) and magnified it, so I could read what it said—Lithium Cell CR 927 3V. I called half a dozen other places where I’d seen batteries sold and none of them carried it. Finally I got one at a store that specialized in batteries. I figured I should learn a little more about these things for next time.


Lithium is used in a variety of batteries because it has the greatest electrochemical potential—it is the best element for giving up electrons, so it makes a good anode (negative electrode). This also means, however, that it reacts “violently” with water or the nitrogen in the air. To become usable in batteries, lithium electroplating technology had to be developed and the safety issues had to be solved, by making the batteries sealed and yet with venting so they do not explode. You definitely do not want to confuse this with candy.

Lithium is used in primary batteries, the kind that can only be used once. Lithium-ion and lithium-ion-polymer batteries are secondary batteries, which means that they are rechargeable.


The C is the International Electrotechnical Commission (IEC) code for the electrochemical system using lithium and manganese dioxide. The manganese dioxide is the cathode (positive electrode) that reacts with the lithium and picks up the electrons. Manganese dioxide occurs in the mineral pyrolusite—the main ore of manganese. The C simply means that this system happened to be third in their list of battery systems—not to be confused with C batteries.

Lithium manganese dioxide batteries have a lot of power packed into them and last a long time. They have a long shelf life and work well under different temperatures. So they make sense to use for our dog light.


The R indicates that it is round.


The number describes their shape. The 9 is for the diameter (actually 9.5mm) and the 27 is for the height (2.7mm). These small batteries are called button cells, although they are much thicker than any of my buttons. The bigger ones are called coin cells.


V stands for voltage. The amount of voltage depends on the system being used. Lithium manganese dioxide batteries are always 3V, no matter what their shape. Other batteries with different systems that are similar to this are only 1.5V. Conversely, things that require 3V are bigger and can accommodate the larger, coin batteries.

If batteries are not included in your thoughts about technology, you might be positively shocked by their potential importance.

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