If the coach master electrical switch (by the entry door) is ON****.......
Coach batteries are charged by either.....engine alternator, generator or shore power .....depends on what is running or hooked up.
Chassis battery....only by engine alternator.
Presumably.....solar charges all the time it can but it doesn't usually have the power to dependably maintain or quickly recharge a depleted battery bank. Solar is a good thing but you need redundancy and back up for power sustainability and longevity when using "juice" in the real world of high demand power consumers like DC refrigerators.
**** some coaches may charge batteries if it is OFF from AC shore or genny. I turn mine on after connecting shore power although you can "hear" the system energize when plugging to shore.
Hot Tip. Turn an overhead light on in the coach you can see from the entry way standing out side facing the doorway. NOW.... turn the master electrical OFF. Light goes out. Now you know the coach 12V DC electrical system is OFF. (The master switch telltale is hard to see and it is easy to forget to turn it off. The overhead light in the salon is a visible reminder power is ON as you close up your coach. )
Another thought. Do you have the One Place control panel? On BATTERY, it will show state of charge for bothe coach and chassis batteries in Volts.
Hot Tip. When you enter the coach..... flip the master electrical ON... (your overhead light in the coach should come on!) Immediately go to the One Place and key up the battery levels. Jot down the values. Good reference data and lets you know the SoC of the batteries.
Start the engine. Go back and key up the battery SoC on the One Place. SoC should be increasing as both batteries are being charged. On shore or genny.....only the coach set will be charging. Solar should have a volt meter to show your input volts and SoC of the coach bank.
What year and model do you have? There is a lot of variation and there are many aftermarket additions too.
Generally there will be a solenoid near the starter battery that has a wire that goes back to the house batteries to charge them. That solenoid is turned on when the engine is running. Sorry, don't have a picture but it will look something like this: