Installing Battery Isolator 08771 in 2002 Ford Excursion

Question:

I am finally getting back to my auxiliary battery project and found our past correspondence. I made a drawing of the proposed wiring and wondered if you or one of your other experts would review the diagram and offer suggestions. Thank you.

asked by: Dean B

Helpful Expert Reply:

The way I read this is that you have a crank battery in your tow vehicle, you have or want to install, an auxiliary (Group 31 deep cycle lead acid) battery that will also be in the tow vehicle with use of the battery isolator to charge this battery. However, in addition you want to connect a second similar (Group 31 deep cycle lead acid) battery installed on a trailer, to this same charge circuit. Yes, the drawing that you have attached shows a circuit that will work for charging the battery on your trailer however, not in the best way. It is that the third battery, the trailer battery, is not always connected within the circuit. Obviously this is because you will not always have tow vehicle and trailer connected but when you do, you are creating a series circuit, a battery bank in which the individual batteries are at different states of charge and this is not best for battery life. But yes this will work.

My suggestion, because you are wanting two G31's with one in the tow vehicle while the other is on the trailer, is to run two circuits. You can have one for each battery and manually connect/disconnect each battery for charging with use of something such as Bulldog Winch Quick-Connect Set, # BDW20047. You will only be charging one battery at a time, outside of the tow vehicle's crank battery, but there's no concern with state-of-charge relative to each other. This will most likely be better on your tow vehicles charging circuit as well.

expert reply by: Michael R