As answered the answer is NO, no battery will ever charge itself. They must be recharged by an eternal source.
Now, if you are in an RV, the ONAN should power the house same as shore power would, (possibly beyond what shore power does, but that's another thread)
This includes powering the CONVERTER which is the device that charges the battery.
So yes, the converter SHOULD charge the battery when the ONAN is running.
What is the make and model of your converter.
Oh, and electronically, no matter if you have a single Group 24, or multiple 4D or say half a dozen six volt in series/parallel.. It's all 1 12 volt battery, though usually with multiple "Jars" we say Battery Bank.