I am measuring the voltage of a 24 V battery using the ADC from Arduino Uno. I use a voltage divider to bring the voltage below 5V (the maximum the ADC can accept).
I noticed that as long as the ratio of R1 and R2 is the same for my voltage divider – it's better to use higher resistance values to avoid slowly discharging the battery. I tried using resistors up to mega-ohm range. What do I sacrifice by using higher and higher resistances? The intuition tells me, that this cannot go forever, because high enough resistor would be equivalent to an open circuit.
By reading other similar questions it seems I might be sacrificing accuracy, but I am not sure, as other questions typically have a different setup.
If it is accuracy, is there a formula for that? When does the standard voltage divider formula break down? Giga-ohms, Tera-ohms? How to calculate that?
I am aware of this question, however the answer there seems very convoluted, comparing load and no-load scenarios (where I don't have any load at all). If that is the answer, I do not understand it.