I am in the planning stage here as well to do something similar using the SMART MODE solenoid HD relays.
The SURE POWER and BLUE SEA SI-ACR Battery Isolators SMART RELAYs are pretty neat units to use to charge auxiliary batteries only when the Truck Start Batteries are being charged in my case...
In the past a Heavy Duty DIODE BASED unit was very popular but due to todays dependence on very close tolerance battery DC charging voltages the high voltage drop of the diode based units does not work well with todays quick three hour smart mode charge specs.
My biggest concern at the moment in my planning is I am hoping my truck start alternator has a large enough OUTPUT rating to handle charging the additional batteries in my battery bank.
I really like to follow some of the original golden rules to never ever mess with the basic truck charging system as this is you last resort on getting back home...
I notice some of the Emergency Vehicle setups around here like to use a separate truck alternator system for the auxiliary battery charging loads.
I will most likely go with BLUE SEA model unit which cost more but has a well known track record on being reliable marine quality units.
I don't have any first hand operational use knowledge here for either of these two units...
Let us all know how your charging setup ends up...
Roy Ken
