You paralleled a dead battery with a charged battery. Bad idea. The charged battery tried to charge the dead battery. That wasted a ton of amp hours.
We do NOT buy batteries. We rent them. If you have an RV battery that is 4 year or older why waste time wondering. That is past its useful life. YES< YES, I'm going to get a dozen people tell me they got 9 years on their batteries with no problems.
I worked with batteries in public safety vehicle for over 40 years, owning a telecommunications company. I am a Senior Certified Electronic Tech. FCC licensed, Motorola Certified.
Save time and misery. Replace old batteries, clean all connections shiny and new. Take care of them. Keep them charged and watered properly. If you have two 12 volt batteries now. I would replace them with two big 6 volters in series.
Now go camping.