There are so many ways to go when monitoring batteries.
I use the DVM panel approach. I mounted this and a push button switch in the bathroom above the 4 led indicating lights panel for voltage/tanks that came with the trailer, I just check my battery in the morning when I am pondering the world.
Mini Voltmeter Five 0.36" Digital Voltage Monitor DC 0-4.3000V-33.000V Volt Tester Panel Meter
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1