Depending on the age of the batteries it may be time to look at replacements.
As to battery configurations Harris Battery had a document on their site a few years ago. If you are an FMCA member late last year thee FMCA Family Magazine had a multi part article on RV electric systems and they went into detail about batteries and battery configurations.
4 12VDC batteries can be connected in parallel in one string. 4 6VDC batteries must be connected in series-parallel (2 strings of series connected in parallel).
Here is the link to the document from Harris. The document is to large to post on the forum. Page 13 has diagrams for the various battery configurations.
https://www.harrisbattery.com/sites/...ide_web2_1.pdf
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