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How to Wire Two Batteries In Parallel on an 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 # TR118665 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 # TR118665 Battery Isolation Solenoid for you to review.

expert reply by: Bob G

Robert G

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