Battery measurement is off

[TokenRat]

What is the problem

Currently, getBatteryVoltage uses a factor for the internal ADC of 3.5V instead of 3.3v, what it should be. The reason is: If we use 3.5 as the factor, when on batteries, we go into soft-brownout detection at around 3.36V, which is right what we want. (Measured with multimeter on the batteries). Why is this? What is wrong with the formular?

Also, when on USB and monitoring serial, we get values which a very off. If we use 3.3 as a factor, we measure almost 0.2V too little. Using 3.5 as the factor still does not get the perfect result.

Maybe someone can spot the mistake…

Code:

ef28-badge/lib/EFBoard/EFBoard.cpp

Line 140 in eefaa05

const float EFBoardClass::getBatteryVoltage() {