NCC XFS

HI, I'm a newbie on here so a big hello to everyone. I had this problem about 2 years ago when I changed the large battery on my 2014 3llr XFS. Tried to find a solution on several Jag forums but eventually took it to my local Jag dealer and they changed the junction boxes to solve the problem. I wonder now if I should have left the smaller battery connected and thus avoided the problem, but too late now!. Cheers Steve