Not sure if this answers your question, but I installed a Flow-Rite system on my Excursion. It allows all the batteries to be filled from a tube, which I place in a gallon container of distilled water.
There is a bulb pump in the tube, and when the batteries are at the correct level, you can't pump any more.
It has worked for me for many years, and is transferable when you have to change batteries.
JT
