Disclaimer: I'm still learning about electronics so forgive me for anything that sounds completely stupid.
My project is pretty simple. I have a single 48V DC battery as the power source, connected to that is a 48V -> 12V DC converter that will power the Arduino. This DC converter is isolated (no continuity between in & out ground pins). However, I want the Arduino to monitor the voltage of the battery, so I have the 48V run through a voltage divider and wire the output of that to one of the analog input pins. As I've found just hooking up the positive to the analog input doesn't work and produced values all over the place. This makes sense as I've read the analog input pins measure with reference to ground, so I run a wire from the ground of the voltage divider to the ground pin on the Arduino.
However, isn't this effectively bypassing the ground isolation of the DC converter? And if so could this cause problems / fry something? What if I only had one of the grounds connected to the Arduino? Will I get inaccurate values from the analog input because of different grounds?
Thanks in advance.