My Trimetric battery monitor is connected to both banks and gives accurate battery voltage displayed to 0.1V resolution. The monitor has millivolt resolution for determining power usage.
My Monaco installed gauges are designed for the salesman to claim what a great battery monitor the rig has. The dash gauge can be used to determine that the alternator is charging the chassis battery.
The Trimetric display or any battery connected voltmeter can indicate the battery status IF you know about how much the house loads are. ie A large draw drops the battery voltage which will rise after the load is turned off. I have 3 charging sources for both banks: charger, alternator and solar.
Most electrical problems are better served with a portable DVM to isolate to the source or maybe a test light. DVMs typically have a long response time and a analog meter has better transient resolution. Beyond that an oscilloscope would be required.
