Battery maintenance while camper is in storage

AnEv942 wrote:
Simply testing volts, any inexpensive multi-meter, analog or digital, will work.
If the batteries are installed in camper, they are already tied together, no need to jump terminals between. Testing one battery will show average of both batteries. If there is no load/charge source being removed-then no need to wait. To test individual health obviously they'd need to be disconnected from each other, and waiting a bit to watch as they stabilize.
IF your disconnect positively disconnects from any parasitic load that will work instead of pulling cables for summer storage.

Many thanks AnEv942. I now understand. This exactly answers my questions.

I thought I had one more question about where to place the test probes of the voltmeter for testing two batteries installed in the camper. But from what you said about the batteries already tied together I looked back at a diagram of RV batteries wired in parallel. The positive terminals are wired together and the negative terminals are wired together. So, it makes sense that I can test from any positive terminal or wire to any negative wire or terminal. It should make no difference because the terminals are wired together, as you said.

So I have been searching Amazon for multimeters. This multimeter seems to have good reviews. I am going to order it unless someone offers a better suggestion:

INNOVA 3320 on Amazon

As to the other suggestions in other replies. I am really trying to avoid needing to take the batteries out during the summer. The batteries are big and heavy and it is difficult to get them out of then back into the compartment. As to solar, it is on my wish list but for longer term. Right now I am trying to figure out what to do right now and for the rest of this summer.

While of course there are alternative approaches I think my plan as described in my original post is the best for me right now for my current specific circumstance. It follows the recommendation in the manufacturer technical manual for my Lifeline AGM batteries, to boost charge after 90 days or when the batteries drop to 75% charge (open circuit 12.5 voltage). Now that I believe that I understand how to test open circuit voltage for that 75% charge level, it seems that question is fully resolved. Thanks to all who responded!