How to Wire Two Batteries In Parallel on an RV Trailer

Updated 07/01/2020 | Published 01/20/2011

Question:

CONNECTING 2 BATTERYS TOGATHER ON RV TRAILER ?

asked by: RON

Expert Reply:

When connecting two batteries together on an RV trailer you usually connect the batteries in parallel to draw 12 volts from both of the batteries. We have a photo, see photo at right, that shows how to wire the batteries in parallel.

Once you have the batteries wired properly in parallel you will need to connect the 12 volt power wire from the trailer 7-Way connector to the positive wire on the first battery. This connection will help maintain the batteries when the vehicle is running, but will not charge them sufficiently from a discharged state. You should be sure your batteries are fully charged before leaving for a trip.

You will need to disconnect the trailer from the vehicle when parked for extended periods, or use a battery isolator, item # PK5231201 to keep your vehicle battery from being discharged if the trailer batteries are being used.

To wire the Battery Isolation Solenoid you will need to splice the side terminals inline with the 7-Way Power Wire, attach a wire that is powered when the ignition is turned on to the small post on the front of the Isolator, and then mount the isolator to a portion of the vehicle that is grounded to the vehicle frame. I have posted a photo of a wiring diagram for the # PK5231201 Battery Isolation Solenoid for you to review.

expert reply by: Robert G

click to enlarge

Terry R.

6/1/2020

Wanting to make a room cooler out of ice chest and to connect another battery in parallel to be certain first battery does not discharge too much. Was thinking to just unplug from truck when using it and if truck into trailer when on road to recharge batteries.do you think that would work?

Chris R.

6/4/2020

I believe you're saying that you will disconnect the battery bank from the truck when you're actually using them (or the ice chest that's drawing power from them) but then hook back up when on the road (which will complete the charge circuit to help maintain their charge). If this is the case, then yes - this will work perfectly.

Terry R.

6/4/2020

@ChrisR yes that is what I want to do Thanks Chris

Clay

6/27/2020

This may be a stupid question.... but what gauge wire do you recommend?

Chris R.

7/1/2020

NOT a stupid question! You want to go pretty heavy when wiring batteries together. Something around 4 gauge should be sufficient but it wouldn't hurt to go larger, either.