Two-Battery Switch setup

Hello people!

Bay area person modifying an old JUCY van and trying to rewire the battery set up:

Here’s my current setup:

flooded lead acid Starter battery and House Battery connected in parallel with a voltage relay

House battery +terminal connected to a fuse box that goes to the fridge, lights, etc,

solar to a charge controller connected to the house battery terminals

what I’m trying to do:

I have a 100ah lifepo that I want to use with the solar and connect to the current house batteries load, as the current house battery doesn’t hold a very long charge to keep the fridge running over night, and has a specific compartment designed for it under the hood next to the starter(where the lithium battery can’t go I assume due to temp concerns). I originally was just going to disconnect house battery and just wire the lifepo battery up to the load, but its nice to be able to run the fridge etc from the house battery when the vehicle is running, so I was wondering if there’s a way to connect both the lithium and the house battery in a sort of diode/mosfet situation that runs a load off of whichever power source has a higher voltage. I would also be happy to just have a switch that goes between the two if the former is too advanced.

Any recommendations of how to wire this?

You should not mix battery types. But they make a switch that allows you to switch battery banks. 1 - 2 - all. They are common on boats.

For what it’s worth you may just be able to run all that off of the starter battery when the car is running. It would depend on how much power your alternator can push.

Thanks! Yea if there’s one thing I know from looking online, it’s to not combine different battery types. The battery bank switch is what I’m looking for!