These lifepartners just gotta warm up to this oldiron stuff ron! And it helps if they don't experience too many breakdowns on the road! We look at that as an adventure, wimminfolk look at it as a disaster and crisis!
Running dual yellow tops is an excellent idear, wish I'd done that looking back when I invested in the optimas. The deep cycle yellows serve just fine as crank batteries, especially on the IH stuff since cranking requirements are so mild! My mistake (I thought I was smarter than johnson controls!) was in mixing the chemistries!
Johnson controls clearly advises to not mix batteries of different chemistry in multiple battery systems. And the isolator folks all advise using multiple batteries that are new and "matched" (meaning they carry the same "lot" number code).
The alternator can only produce one "charge rate" and that is based upon the most needy battery in the system. A single alternator can't charge at two different rates, and the isolator only prevents a low voltage battery from discharging a "charged" battery in an attempt to equalize charge level chemically.
In my case, I made the sitch even worse! I had a red top and a yellow top combined under the hood, the proper "terminal voltage" between those two chemistries is significantly different as to what constitutes a fully "charged" battery.
Then...when the trailer is connected, that added into the entire charging system, two additional batteries, one was a conventional flooded cell deep cycle, the other a red top. Total wrong combo! So charging four batteries off a single alternator through an isolator is really dumb! Yes, the alternator is perfectly capable of doing this (and did so for nearly three years), but only the red top crank battery was ever fully charged at any one time when driving down the road.
When the trailer is plugged into shore power, the on-board charger charges the house batteries at the proper "rate", but since there is no isolator on the trailer from that end, then the mismatched batteries also would not allow the red top to fully charge as the chemistries are significantly different!
In that case, the only thing I did right when the trailer was plugged into shore power, was to disconnect the trailer harness so the trailer charge could not attempt to charge the tow rig batteries. To run the four battery setup, I should use two isolators, one mounted in the trailer system.
When I hit the lottery, I will have four matched optima blue top sparkers! Two under the hood, and two in the trailer...that is the ultimate "dry camp" weapon! That's about $800 in batteries right now locally! That gives me three batteries for the trailer, and keeps the crank battery out of the loop for discharge for long-term dry-camp.