Which monitor did you get? It looks like a simple + and - battery voltage connection.
The problem with trying to pick voltage from the Thor display panel is; that voltage is coming from the DC buss, not the house batteries. If you want a battery monitor you want to pick the voltage straight from the batteries through new wires. The wires carry almost no current so the smallest telephone or network wires would work.
My monitor is a current monitor as well and uses a shunt at the batteries. I also have an AC side monitor (voltage and current). This is my installation; the monitors are inside a flip-up cover. Why would I put monitors inside a flip-up cover? You may ask? Because my wife is a cave sleeper. Any light, even little LED displays "penetrate" her closed eyelids and keep her awake.
So that's for her convenience.