Lewgillett- it was the start batteries that were replaced. I did not know the van had 2 start batteries until I took one out. I am shopping for a house battery now that will fit in the bracket. I just want to get one so I can start using the van and fixing all the electrical things going on. I'll upgrade the batteries and bracket later. I have learned so much in the last week.
I got it direct from sportsmobile so it would be the exact size to fit in. All the replacements I found were physically smaller and I would have had to patch in the larger hole and carpet as mine was along a kickboard just off the floor...
Your house battery will never recover from getting that low. It will show voltages of 13.X after charging but it won't last more than a couple of hours. You need to replace it. Typical things that will charge it is leaving the inverter or converter ON when there is no shore power or solar in excess of 2 amps. You have jumped in at the deep end so get the Manual from the SMB web site.
I want to say thanks to everyone for your help and suggestions. I'm getting the hang of how the van's electrical system is put together.
I replaced the house battery with another D4 AGM because it fit and was available. It seems to be working well. I will probably upgrade the house battery in the future. I read through the suggestions and research that you shared. Very educational. I will use them when the time comes to upgrade. Thanks!