Ok....lets say you wire two 12 volt, 100 ah batteries in parallel giving you 12 volts, 200 ah's.  My question is, can you wire one 12 volt, 100 ah battery to another 12 volt battery with lets say 80 ah? 

You can but your bigger battery may use some of its energy on the smaller.

Yes, but the batteries will not discharge evenly. That’s like putting a D battery in parallel with a AA. The smaller battery will run down voltage faster and pull voltage from the larger. It’s not ideal so don’t plan to do it forever. 

^ What he said.

That's what I was kinda thinking myself but thought I'd asked. Thank you guys.