Hi!
I'm having issues with inconsistent battery readout results. I'll elaborate more below, but in general, I have multiple devices which 'sleep' most of the time, and when they wake up they measure the battery voltage using the SAADC, translate it to battery %, and report it via BAS. My problem is that within a few hours, with nothing major changing, I can get an enormous variance in the battery % values reported. The voltage is read before any peripherals draw current, before advertising starts, the batteries are placed in a control environment so the temperature is constant, the code they run is constant, and there is nothing else I can think of which can affect them.
My devices use: nRF52840, CR2032 batteries (~3V). No relevant peripherals draw current until after the SAADC read is completed.
To get the battery %, I use the SAADC with pre-scaling 1/6, 10 bit resolution, reference voltage 0.6A, I use the linearization formula suggested here for the CR2032 curve. While I understand the curve may be inaccurate in terms of it matching reality for my specific battery, I should still expect it to give me consistent readouts- i.e, that the battery % values given should be ballpark accurate, should not increase sporadically, with minor fluctuations etc.
When I try to read the ADC multiple consecutive times with 1 ms sleep time in between them, I get a small variance between the results, lets say up to 5%. its only between different reads in different wake ups, where I see this large gap between measurements.
I'm not sure what could be causing such a large variance in the measurements, and would love it if someone could point me in any possible direction.
Here is an example of the values I'm logging:
Day0 08:36 - ADC value 849, Bat 90%
Day1 14:55 - ADC value 827, Bat 48%.
Day1 14:56 - ADC value 839, Bat 73%
Day1 14:57 - ADC value 844, Bat 83%
Day1 15:26 - ADC value 802, Bat 30%
Day1 21:27 - ADC value 785, Bat 21%
Thanks!
