Roadtrek E-Trek Battery Replacement

[photolimo]

We recently went on a short trip with our 2014 rig and had some troubling issues with our batteries. Everything seemed to be dead 12v and 24v. When we returned home they were still dead a few minutes after driving/charging all day. We checked the voltages of the individual cells and the batteries that were connected to "Balancer" were totally dead.

The service center near us installed a "battery balancer" next to the solar charge controller and replaced the bad cells.

Finally, my question. Is it possible that more than just the two batteries need to be replaced? How would I check them to see what state of health they are in?

Here is the battery setup we have: https://docs.google.com/drawings/d/1...it?usp=sharing