A battery monitor with a shunt will give you the best results of what is going on with your batteries. The trouble with a shunt is ALL negitive wires need to go through the shunt.
When I did my recent solar upgrade I installed a shunt for the Victron battery monitor. Only to find that that different systems in the rv used different points on the chassis to connect to ground. All of thos3 had to be rewired to the shunt for proper monitoring. Only my 2 cents