Can I connect my “solar batteries” to use for the RV’s house battery?

Dear Dave,
Instead of replacing the house battery under the hood, can I run a cable from my 600-watt solar system batteries (2 x 100ah) I installed in the basement to the cable that powers the house lights? (There are 3 positive cables going to the under-the-hood house battery. I found which cable powers the house lights.) The space for the original house battery is a very odd size 5.5″ wide x 12.5″ long x 9″ high. —James, 1996 Jayco 295 SB

Dear James,
From what I can tell, your Jayco is a Class C on a Ford E350 cutaway chassis and would have two different 12-volt battery systems. The first would be called the engine battery that will start the engine. The power is classified as cold cranking amps (CCA), which is an initial burst of power to turn the engine over. The second is the house battery system, which consists of one or more deep cycle batteries classified as available amp hours. It is designed to run the house components and be drained down to 50%, then recharged, which is what the “deep cycle” refers to.

Typically, the engine battery is located in the engine compartment and a 1996 would probably still have the old top post connections. House batteries can be found in several locations such as under the entrance steps, in a small compartment on the outside behind the passenger door, or even in the engine compartment. The house battery or batteries are wired to the distribution center inside the rig. It has automotive-style fuses that provide 12-volt power to the interior lights, roof vents, water pump, and appliances that run off LP such as the refrigerator, water heater, and stove.

From the photo you provided, it looks like the original house battery was in the engine compartment, since it has the flat connections that normally bolt on to the threaded posts. You stated that you have installed two 100 Ah “solar batteries” located in the basement to power the lights. This is confusing, as there should not be a battery bank that just powers the lights and another house battery. I believe the battery that was in the tray of the photo was a deep cycle flooded lead acid house battery that went to the distribution center. The only company that I have found actually promoting a “solar battery” is Go Power!, which offers a 100 Ah AGM and 100 Ah Lithium Iron Phosphate.

There are others that are marketing solar compatible, but these are not really a “solar battery,” just a regular AGM or Lithium Iron Phosphate battery being paired with a solar charging system. I also assume you installed a solar panel on the roof or a portable wired through a charge controller (hopefully) and to the two new batteries in the basement. What I wonder is how you wired them to run just the lights, as the wiring for the lights would be connected to the 12-volt fuse in the distribution center. The two new batteries should have been wired to the main 12-volt bus bar in the distribution center that would power all the 12-volt components. That would be your house battery power and no need for the battery in the engine compartment.

In the photo you provided, there is a positive and negative cable with eyelet connections. However, there is another cable with the wires twisted, which I assume is a positive cable that goes to some other component and since it does not have a hard connection would be an aftermarket component? This could be a radio, backup camera, or something added after production, so you would need to track that down as well and connect it to the new batteries or the distribution center.

I would suggest wiring your two new batteries to the distribution center to power all 12-volt DC components. You should be able to trace the unconnected cables in the engine compartment to the distribution center. However, the positive cable most likely goes to a solenoid first, commonly referred to as the Battery Isolation Management (BIM) solenoid. This provides a jump start from the house battery to the engine battery, if needed, and also provides a charge from the engine alternator to the house batteries while driving. If you installed lithium batteries, you will want to check what voltage you are getting from the alternator as some will be as high as 15.6 volts, which is too much for lithium. Most want 14.6 volts. However, if you have the Go Power! version, it does have a Battery Management System (BMS) that helps regulate overcharging.

If you can provide a little more information, we can hopefully get your house 12-volt system operating properly.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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