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CR2032 battery voltage with BLE
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jmaja:
This paper shows that the actual leakage currents are quite small: https://nepp.nasa.gov/files/24732/2013_n239_Teverovsky_ESTEC_MLCCs_paper.pdf

Typical currents are order of magnitude smaller than specs. And even then it is mostly absorption current, which will level down to the actual constant leakage current. E.g a 22 uF 1206 6.3 V MLCC had only a few nA leakage after one hour at constant 6 V. Due to absorption the current was about 1 uA at 1 s and 0.1 uA at 10 s.

How did Rerouter measure the leakage, since it seems to be a function of time? One hour is a short while, if the device is left to sleep for days.
David Hess:

--- Quote from: jmaja on March 18, 2019, 05:33:29 pm ---Thanks David for the link. Lot to read.
--- End quote ---

I was too much to repeat here so I just gave the link which includes all of the links.
jmaja:
Here is a new battery voltage graph. It includes the earlier one. The spikes to 2.4 V are not real, I just used them to mark where the sensor was not active and therefore started again with normal current consumption. At about 19 hours there is a spice up, which is caused by the programmer. After that the bugfixed software is used. Betweeen 10 and 12 hours the device was outdoors in 5 C and with the software not working as expected. This can actually be seen by the too frequent battery voltage variations. It should have measured only once per 64 s, but it measured at 4 Hz.

Now with the software working OK the voltage dropped only to 2.75 V in 12 hours. With multimeter it is now 2.93 V and oscilloscope shows 380 mV voltage drop and 10 ms average being 120 mV below the average. It seems ESR has increased again. 44 ohm? The peak fall time to 1/e delta is about 1.65 ms, which should be RC. From that R would be 33 ohm (using 50 uF). Anyway rather high value for a battery that should be almost full.
Rerouter:
I measured my leakage by having the 2 active IC's lifted off the PCB and powering the board through a clone of a uCurrent, I only checked it for about 20 minutes at a few different temperatures, (-15 to 65C)

It may have been other factors, and may well have improved with age, but It was mostly idiot checking, To make sure that I put the other chips in there correct sleep / power down modes after recording the baseline.

Also how exactly are you calculating your math,

Using my little falstads calc, its looking pretty close to 15 ohms ESR to match the drop your seeing, though arguably seeing the scope screen shot would help,
Psi:
There is quite a range of ESR between different brands of CR2032 cells

When new they can be from 20ohms to as high as 120 ohms.
And they get much worse when they start to get flat.
(Panasonic brand cells are quite good and around 20ohms new)

The high ESR makes your voltage readings very inaccurate especially if you measure it at the end of a high current period.

Add some smarts into the code so it only reads that battery at a known time when nothing else is running.

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