For years I went with dual batteries now I run dual batteries wire together in parallel with no controls or expensive dual battery systems and carry an antigravity jump bag. Twice the available capacity as your standard dual battery set up with the back up of a small jump bag. Now with drawing from both batteries at the same time I get much lower over nite discharges and my expensive batteries should last much longer.
I run the same set up. and it works great. If you have dual batteries, with or without an isolater, if one goes bad, both need to be changed out at the same time. If you buy 2 batteries at the same time for the vehicle, in my experience, they will warranty them both if one goes bad. I have had this happen in my650 and my diesel van in the last couple of months. Both AutoZone and Sears were no problem.