Nick --
Your Allegro Red is built on Freigthliner XCR chassis - correct? Are the engine batteries original? If "yes", those batteries are very likely Alliance brand (Freightliner's brand) traditional Group 31 flooded batteries, not AGM batteries.
Just a month ago I replaced the OEM Alliance batteries for my motorhome's engine and opted to purchased flooded-type NAPA Group 31, 1150 CCA commercial batteries and not spend $120+ more per battery for AGM type. My logic on purchasing the traditional flooded batteries is the engine starting batteries do not need maximum reserve power like the house batteries need (my house batteries are AGM type). I purchased the NAPA batteries from my local NAPA store. The store honored the "on-line" special pricing at the time for those batteries.
Here is the link to the batteries I purchased -->
https://www.napaonline.com/en/p/NBP7...ndex=Universal
Hope this info helps!