Combining battery sizes in parallel.

I know all the doom and gloom warnings, but let me give you a bit of practical experience. We had a 2008 Allegro Bus with 4 flooded 6v batteries as house batteries. Since we boondock a lot, I wanted something better. I split the DC bus and added a forward inverter so the high draw items like satellite TV, satellite Internet and Entertainment center were on the front system. I then put 4 AGM 6v batteries in the main house battery bank and moved the 4 flooded batteries to a newly constructed rack under the front cap to feed the forward AC inverter. In order to keep all batteries charged I set up a power relay that allowed me to parallel both sets of batteries so they could be charged from shore power, the generator or the engine generator when the Bus engine was running. This relay also allowed us to use all 8 batteries to power all DC items on the RV. That setup worked just fine for over 2 years and with heavy use.

Again, this setup was against all "accepted" reasoning and recommendations I could find. My suggestion to you.... Try it and see if it works for what you want to do. What "EVERYONE" knows and what works are sometimes very different.