As per owners forum, the chassis batt on your rig charges off the alternator and the coach batt charges off the converter while plugged into shore power or the genny.
In case you fire up the genny and you don't have power.... There is probably an on/off switch when using the genny vs shore power to power up the rv. On my rv I don't have a switch, I have to plug the genny into the 30amp receptacle that I also use to plug in my shore power.
You could use an inexpensive volt meter to test the batteries. Then start the rv and see if one or both the batteries charge.
With the rv off those batts might read 12.6v. As soon as you start the rv, that voltage will jump up to 13 - 14v . That way you'll know for sure if the alternator is charging one or both.
๐If the set up is not what you desire, then you could always add an isolator module under the hood that will charge both batts when driving and only draw down the coach batt when camping. It acts as a one way gate so you don't kill both batteries while camping.
http://www.thorforums.com/forums/f8/chateau-sprinter-chassis-battery-issue-704.htmlHave those batteries load tested. You might need to buy new if its not holding a charge. That way you know what you have. If you decide on 2 new coach batteries , buy the same size and same age (checks the dates of mfg.) that way you will know they are in balance and will charge and discharge at the same rate without one weak batt pulling down the stronger batt.
Some people run 2 -12v batts and some desire 2 - 6v batteries in series to = 12 volts. Research that to make your decision.