Hi all,

I bought a 2001 V10 Club Wagon a few years ago and mostly use it for camping and adventures. I haven't done any modifications to it, but recently started thinking about adding a house battery to power a refrigerator/freezer and my CPAP sleeping device. As I'm looking into adding a deep cycle house battery I was crawling around under the van and spotted a second battery under the passenger side frame rail behind the side door. My first thought was that this was connected in parallel to the engine compartment starter battery to assist in starting the van. I pulled the battery down and it was the original motorcraft battery from 2001 and it was completely dead. I replaced the battery with the same battery as in my engine bay thinking it was a secondary starter battery. Now I'm not so sure. The aux battery is wired to a relay under the engine compartment battery and I've been seeing online that the battery is for towing and trailers (I don't know much about towing and trailers). What I do know is that I had full function of the van and it's electrical while this aux battery was completely dead.

Looking at the wiring diagrams is a little confusing:
-Page 13-1: Power Distribution, shows the Engine compartment battery and aux battery in parallel
-Page 20-1: Starting System, it only shows the Engine Compartment Battery.
-I don't see anything about the aux battery relay or i am missing it altogether.

What I would like to do is disconnect the aux battery from it's circuit and wire it as a direct parallel to the engine compartment battery. This has a couple advantages but the primary one in my mind is i will have more starting energy if my kids leave on an interior light while we are in the wilderness (has happened before).

Does anyone have any thoughts the actual wiring and purpose of the aux battery and my idea to rewire it into direct parallel with the engine compartment battery?

 

I haven't looked at any diagram, but would suggest you keep something in mind.

If you have both batteries connected in parallel all the time with the one in the engine compartment and the kids leave something on both batteries could be dead and I don't think you would want that.. I would suspect the relay is supposed to close when the engine is running to keep both batteries charged and when the key is turned off the relay opens and separates the engine battery from the aux battery. You no doubt will need a new aux battery and verify the relay is working.

 

Thanks for the response. I do realize that the plan isn't foolproof by any means. I'm not sure I get any benefit from the aux battery if the relay doesn't allow it to assist in starting the engine.

 

Without looking at a diagram, all you need to try is see what in the camper works if the aux battery is disconnected from the engine battery.

Not that familiar with camper set ups.
Hopefully someone with good camper experience can better answer any questions.

If all the camper power is taken from the aux battery, you wouldn't want that to draw power from the battery that you need to start the engine on the vehicle unless you use power from the engine battery when parked.

 

Batteries are rated as to how many amps they can supply for a certain period of time (AmpHrs)

You would need to know how many amps any accessories draw so you would have some idea of how long it can supply power.

Even if you ran the aux battery down (discharged) it would not affect your starting the vehicle engine. Pretty sure that is one of the reasons the relay separates the batteries when the engine is not running.
You would be able to run more accessories when the engine is running AND the alternator can meet the required power consumed. This gets into a whole new area.