Voltage of 3 V batteries [closed]

Question

I ordered 3 V CR2 batteries. Actually they are 2.92 V and 2.93 V.

Should I consider them faulty, or is this difference from the nominal voltage acceptable?

Answer 1

They are likely fine. Batteries are not constant voltage sources. While the the chemical reactions that liberate their stored energy "create" the same voltage as they proceed, reaction products build up and increase the internal resistance which has the effect of lowering the voltage at their terminals. Take a look at this discharge curve for a Duracell 2032 battery with different resistance loads attached to it. You can see that they all start out at somewhere above 3V, rapidly drop to somewhat below 3V, and then gradually decline until the battery is "dead" and the voltage starts to drop rapidly. Battery powered circuits are (or should be) designed to deal with these changes in voltage. Image source: https://media.digikey.com/pdf/Data%20Sheets/Duracell/CR2032.pdf

Answer 2

Usually, 3-volt batteries come higher than 3 volts. Get a battery tester and see what it says. Harbor Freight's cheapest multimeter (sometimes given away free, $5 last I checked) has a battery tester built in. Internally, they use a 360 ohm resistor across the battery and measure the current. A healthy 3-volt battery should pull 8.33 mA according to this scheme. If they draw only 6mA, I would ask for a refund.

Looking at this graph from an Energizer CR2032 datasheet:

You should see highlighted in orange the pulsed test current-vs-voltage curve, and that 400 ohms was used for the test (at 2 seconds pulse, 12 times per day). If you test with the suggested 360 ohms, it should be an acceptable test. The cutoff voltage for this CR2032 is 2-volts, which corresponds to a draw of 5.55mA through 360 ohms.

You can also measure the voltage of the CR2032 while you're testing it, and see how low its voltage drops. The manufacturer Energizer considers their CR2032 dead at 2 volts.

Here is what your test should look like:

Internally, a true battery tester does this, so you won't see the resistor. But you can do the above with a regular resistor and get the results you seek -- a true and correct answer! Just set the meter to measure volts while the resistor is across the battery as shown.

For example: The voltage measured determines the current flowing in the resistor. V=IR, so I=V/R = (voltage shown on multimeter)/(measured resistance of resistor). Let's say the voltage shows as 2.5V and the resistance you used is 500, then 2.5/500 = 0.005 = 5mA. Since the manufacturer has determined that 2V is the cut-off, and 3V is nominal, and 2.5 is right between them, you probably have less than half the life of your battery left with the numbers of this example.

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Here is a link to the Harbor Freight multimeter that I mentioned, and here's a picture with the switch setting highlighted: