Coin Cells in Parallel Having Different Voltages

Clean the cells, the oils on your fingers will give you grief.

Cheers

w

I have 10 sets of a setup that's 2 CR2032 coin cells in parallel supplying to a 13Kohm resistor (1% tolerance). I started with brand new coin cells with voltages around 3.1V individually which I measured prior to put them in parallel. The coin cells are seated in coin cell holder which I've bought. I monitor the voltages at the resistors daily and after about 35 days later, I see varying voltages between different sets. Some stays around 2.9 and others around 2.8 or even lower. I measure individual coin cell voltages on sets that has the lowest voltages. I found there are differences in voltages between cells. 1 cell could be at 3.0V and the other cell could read 2.7V. Also I noticed that when I tried to measure the voltages at resistor, the meter reading is not stable, varying from 2.7 to 2.6 and 2.5 by the second. Can someone please explain the phenomenon I am witnessing here?

** FFS what sort of DC voltmeter are you using that has only 0.1V resolution ??

Even the cheapest 3.5 digit meters have 0.01V resolution on the 20V range.

The last digit on a DVM display is always subject to +/- 1 digit uncertainty.

And make sure your probes are very clean too.

.... Phil

Could it be contact resistance of battery holder or internal resistance dif ferences between the 2 cells rather than the oil you are talking about? Mos t people replace coin cell batteries without using gloves or knowing needs to clean the oil off. The data sheet for the battery holder says the max CR is 30M ohms, I just read now.