See Level will tell you voltage. https://www.garnetinstruments.com/rv-shop/products/
You can get into extensive battery monitoring with something like the Trimetic. Trimetric TM-2025-RV Battery Monitor System
Your current monitoring is by way of stainless probes at different heights in the tank. Voltage is transmitted through the water to determine level. The reason they fail is because of sludge or debris on the probes prohibits reliable completion of the circuit.
The See Level system works from the outside of the tank by sensor strips that you stick on. You can use the same wiring from the probes to hook up the See Level.
I have not yet installed this system, but I will be. The reviews that I have read have all been favorable and sounds like they are consistently accurate.