The Battery Control board was supplied by:
R V Custom Products
14000 Anson Avenue, Santa Fe Springs, CA 90670(562) 921-8353.
The interconnect relay (left side of the schematic) is very likely the issue, however the relay is controlled by the circuit board.
If you decide to change the relay go to Amazon and look for a 12V continuous duty relay, may be a "Golf Cart" item, around $30.00, not the $70.00 listed on the RV Products web site.
Hope this helps.
Fred and Bonnie
2005 Dolphin LX 6375
Abby, Ruffles & Scarlett, "The Cats"