Combine or Replace RV House with Lithium Solar System


New Member
Sep 3, 2021
I have a travel trailer with a typical FLA house system - runs the lights, water pump, etc. I have installed a separate lithium solar system that powers our laptops, phone chargers, etc. The solar system is 200aH and 400W panels so its more than enough for its current purpose.

That was my first phase in this project and it works well for short times but the FLA system runs out after a couple days without any charging. My intent was to combine the house and solar systems into one that is powered by the lithium/solar setup. I would keep one FLA battery to set off the trailer brakes in case of a breakaway (from what I have read that's better than also using the lithium for that.)

However, I have two constraints. First, I am not an electrical systems expert and I want to avoid messing with the bits I don't understand. Second, I am not going to my grave with this trailer - I will sell it eventually and when I do I want to be able to cleanly remove my lithium/solar setup and put it back to how it came.

Following is my original plan and a "I'm having second thoughts" plan. I would love to get this community's input on what you think would work best and any help where I have knowledge gaps.

1) Just disconnect the house system from the FLA and connect it to the Lithium leaving the FLA connected to the breakaway brake system. This was my first plan and would involve running the positive from the FLA batteries (which is up near the tongue) and instead into the trailer where my lithium is - easy. However, the negative of the FLA is bonded to the chassis so I am ASSUMING that I need to disconnect the negative of the house system from its chassis bond and run it back to the lithium as well. The problem is where the negative is bonded to the chassis there are two wires both black and one thicker than the other. I cannot trace them back up to know which is which (could the thinner one be ground for the 120v system? Its black, not bare copper). Also the wires just barely poke out from the underside to its bond with chassis so there is simply not a lot of wire or space to work with.

Or is my assumption about the negative wrong? Can I bond the negative of the lithium battery to the chassis for the legacy house system but leave the negative of my solar system still direct to the battery? Can those two methods be mixed? This is where my knowledge fails as I really don't understand the electrical principles only that there are two methods of dealing with the negative: chassis-bond or direct to the battery.

2) Keep the two systems separate and solve the charging of the FLA either by installing a separate charge controller so the solar panels are charging both lithium and FLA. Or keep the solar tied only to the lithium but have some kind of DCtoDC charger (like renology's 20A charger) to have the lithium charging the FLA safely.

Thanks for any input you can offer.


Participation Medalist
Nov 5, 2019
Silicon Valley
Or keep the solar tied only to the lithium but have some kind of DCtoDC charger (like renology's 20A charger) to have the lithium charging the FLA safely.
This would be the easiest and likely carefree. I would get a better DC to DC charger like the Victron Orion but that's only because i like reliability and a long warranty.