I think I will stay with my BLUE SEA SIACR 200AMP Smart relay design but I can see where it is going to have the problem of not really sensing the charge state of the auxiliary batteries and only charge when the truck start battery demands it. I do have the manual switch idea going for me to switch in the auxiliary load batteries manually when I need to. At least the auxiliary batteries would get a 13.6VDC charge during that period. I can also change to the Sure Power 1315-200 Battery Separator which operates under the same voltage sensing idea as the Blue Sea SIACR does but don't really think this would gain any thing more on when the auxiliary load batteries are being charged. Both of these Sure and Blue Sea units will totally disconnect the auxiliary batteries from the truck start battery to prevent draining it down if the voltage drops to a preset voltage.
I am not so much concerned of having the truck alternator do a real big re-charge of the two auxiliary batteries mounted in the truck bed area as these two batteries will have alternate ways of being re-charged with the connection to the RV trailer converter/charge system or from my portable B&D VEC1093DBD running off my 2KW generator if I get caught running down the auxiliary batteries from the use of the two way radios in the truck. My 2KW Honda generator is always in the tailgate corner of my truck - it goes where I go.
I am also a bit leary of using the truck standard alternator to charge the additional auxiliary batteries not really knowing if I am going to overload the alternator or not. Rule number one is never mess with the horse that gets you back home.
At least I will have a couple of PLAN-B methods available to me to keep going
Enough of my problems hehe... Interesting reading since the subject was all brought to life again. As usual nothing comes easy anymore. My old JEEP DAYS method of using diode based battery separators sure doesn't do well these days with all the smart mode charging techniques around us. The voltage drop across the high current diodes sure kills all of that.
Roy Ken