Trying to sort out a charging issue on 1988 Chris Craft 425 Catalina, 454 Crusaders - voltmeter indicates both engines charging only 11v at 1800 rpms, low voltage message on radio/gps when adding any additional load (tabs, auto, etc.). DC panel shows both batteries at full charge 13.25v. Recently replaced SB alternator due to overcharging. What to check first?