Simplest battery monitor and shunt? Advice for non-expert

To me the "most basic and inexpensive way" to monitor your battery voltage inside your TT is to run a pos and neg wire from your battery and terminate the wires on the front wall of your TT and check with your multimeter. I put mine on an inside wall with a std bolt head for neg and a Philips head for positive. Above this I have a chart showing what the state of charge is by voltage readings. It was a no cost way to monitor my battery SOC.