Why go through all the complication for a simple voltage monitor?
It's more things that can potentially drain the battery if and when it goes kaput.
If I really want to monitor the battery, I would just plug in a voltmeter for the cigarette lighter - something similar to this =>
https://www.amazon.com/Battery-Charg...SNBKMCK79Q9ZCT Or just use the secret menu if I don't have a meter at hand.