Paul, I may not be the best person to answer this but I recently had a similar experience and found that the battery cables on the house batteries were corroded. I was at a repair facility in Eugene, OR and the mechanic diagnosed this as being a problem with my batteries. As a long-ago, ex-service manager I checked this out on my own and noticed the corrosion. Even though the mechanic, who insisted new batteries were in order, was reluctant to take the advice of an "amateur", did as I told him. That little correction eliminated the need for several thousand dollars in new batteries. As I understand it the mechanic is no longer with this company. This occured in August of this year. I have not had a problem since.
I am sure someone else (Jon?) will jump in and give you some more help and maybe better advice but this is what worked in my case. It certainly won't harm anything to check this out where making ill-advised adjustments might harm the batteries by overcharging them. Good Luck!!

Darl