The 2020 Magnitude and Omni comes with two 6V batteries and they designed the tray to hold four batteries so I decided to install two additional batteries.
I purchased two Duracell SLIGC115 6V Golf Cart Batteries at Batteries + Bulbs for $117. This is a better Ultra series with a 230Ah rating. They are also manufactured in PA and not China. When I purchased the coach last October one of the first upgrades I did was installing the much better Progressive Dynamics Converter / Charger. It can charge battery banks of different capacities so I was not too worried about the stock batteries being 215AH.
I purchased a Blue Sea Systems 300 Amp m-Series Battery Switches from Amazon so I could disconnect the batteries, use one bank or use both banks.
I also purchased a 3/8" 4 Stud Power Distribution Block BusBar because Thor used a single post right in the middle of the battery tray to connect several positive cables. I wanted to use this to relocate to the side wall of the battery tray.
I also purchased Spring Hatch Holder to hold open the step when working in the battery compartment. I always found it a pain trying to keep the step open all the way when trying to work with both hands in the battery compartment.
During this process I also fixed what I think was the problem with my Battery Isolator (BIM160) working properly. I have had issues with the alternator charging the house batteries when driving and having the Inverter on for the fridge.
According to the manufacturer of the BIM160 it doesn't matter whether the BATT A post has the chassis or house batteries connected to it. Thor connects the house batteries to the BATT A post and the chassis battery is connected to the BATT B post on the BIM160. After doing some research I found that other RV manufacturers use the BATT A post for the chassis battery and the BATT B post for the house batteries.
After I switched the cables I found my Battery Isolator to be working much better. The alternator would start charging the house batteries when they dropped below 12.6V and when I am on shore power I can now hear the relay switch so the chassis battery chargers when it drops below 12.6V. Besides the house batteries not charging off the alternator the way I thought they should I never heard the relay engage to charge the coach batteries when we were on shore power for several days.
After moving some wiring around and replacing the single post with the 4-post BusBar and relocating it to the wall of the battery tray, I got the two new batteries installed. There is plenty of room length-wise in the tray but just enough room width-wise for the four batteries. It also took a few attempts and a little maneuvering to get the fourth battery through the step opening and into the tray. I had to spread the batteries apart as far as I could to finally get the last battery into place.
I was going to try to mount the Battery Switch on the tray side wall but it was just a little tight and with the 2/0 AWG cables attached it is not going to bounce around or go anywhere.
Here are some picture of the finished product: