They arent common oem equipment on rvs either but i think they should be standard there
Most RV's have a battery level monitor built into the panel you check the fresh and black water tanks with. Granted, these are just voltage testers and just give a basic showing of voltage level, but to be honest, a lot of people travelling in RV's don't even know where the batteries are in their RV, let alone know what they would be monitoring with a true monitor.
That's great that you like them and know what you are looking at, but it could be considered helicopter parenting for your RV. Just over monitoring constantly and expecting something wrong to happen.
But it's easy to tell when your lights get dimmer and know you have a problem.
And yes, a good monitor would tell you which battery is giving a fit in your system, but that will cost $$$. If you want the app on your phone so you can monitor it while away, that's $$$$.
I'm perfectly happy with opening the side door, looking at the cheap solar controller, seeing if the voltage is where it should be, starting it once a month and calling it good. But I also have the knowledge and tools to test the batteries and see why there is a problem when it arrives.
For my situation, a complete system battery monitor system just doesn't make sense, pound per pound.
But if I was living in an RV and boondock alot, and depend on the batteries 90% of the time, then it would make sense.