Depending on what kind of disconnect is on it, one type is adjustable. Sounds like there is either dirty cables or a bad draw on the system.
What i did was clean the cables that connect all 4 batteries. Both positive and negative. The had alot of corrosion on them and were blue greenish. I scraped and got all the crud out of them and brought the copper back out for better connection. Just if you do decide to clean them, take a picture of them to properly arrange them back the way they were...id clean even the nuts holding them down as well
