I've been crawling these forums and using google-fu to no avail. I have an Arduino connected to my boat, which operates on two 12V batteries (House & Starter). Those batteries are connected to everything via a power switch, which can be selected to 1, 2 or BOTH (see diagram below). The Arduino is therefore powered by either, or both, batteries at various times.
I am trying to figure out how to monitor the voltage of both of the batteries, but from what I have been able to ascertain is that you can't measure the voltage of the battery if that's also the Arduino's power source... or at least not without something more than what I have. Is there a feasible (or better) way of doing what I'm trying to do?
Thanks in advance!