Your wrong of course - and I'm a retired EE as well. But that degree certainly doesn't make one an expert on RV converters.
If one has a modern 3 stage converter, it charges the battery(s) just fine. It makes no difference that there are more than one or that a few accessories are on the same circuit. This is in part because the battery takes what it needs.
The proof is in the fact that these converter/chargers are working just fine for hundreds of thousands of RV's. If you want to get more technical, further proof is in the measurement of said batterys specific gravity.