I have a 2019 RED 37BA and have upgraded the house batteries to lithium last summer 2021. My rig is using the Magnum remote ME-RC50 panel ver 2.8 which doesn't have direct lithium settings. I am using the CC/CV settings which are working fine as far as I can tell. My rig also uses the Magnum AGS. All of which is working great.
I was looking for a real drop in solution. I went with 4 - 12v OWL Max 2 batteries from Big Battery.
Several reasons for that choice:
1) Lots of power each battery is 228 amp hour for 912 total.
2) They fit my battery tray at 21” x 20.5” and height of the basement.
3) I was able to use the existing battery cables. I used the combiner box that they also sell. The RV cables connect to the combiner box and the combiner box connects to all of the batteries.
4) The weight ended up about the same as the 4 factory flooded lead acid golf cart batteries.
I did disable the battery merge feature. So my house batteries are limited to charging via shore power, generator and/or solar. The Tiffin Battery Merge Spec – 08.16.2016 (which I believe is a Spyder module) appears to be hard wired for a lead acid profile. I am still running the AGM chassis batteries. I don't believe connecting these batteries of different chemistries would be good. Plus I don't think it would be good for the coach alternator (the lithium batteries would likely pull too much power). So I unplugged the line from the power control module to the merge solenoid (which can be easily plugged back in if needed). Now I sometimes see that the coach thinks the merge is engaged but without the solenoid it doesn't really happen. I was thinking of installing a DC to DC charger but I haven't really found it necessary. The house batteries have so much power that keeping things running while on the road is not an issue.
I am working toward being able to run one of my a/c units off of battery. I have recently upgraded the Magnum Inverter/Charger to the 3000w hybrid model. I am in the process of installing a soft start on the a/c and a switch to move the unit over to one of the inverter circuits when I want to run it off of battery.
Here are some pics of the battery install.