Who's in charge?

C&J wrote:
When the motorhome is plugged into shore power AND the engine is running, are the house batteries being charged by the engine alternator or by the converter off shore power?

Both sources of power generate 12+ volts of electricity and are both connected to the house batteries. The converter directly and the alternator through either a solenoid or an isolator.

I expect that the alternator has a higher output rate than the converter. I also suspect that the slides use more amps than the converter puts out.

I expect that the low voltage indication was a result of the two systems having different types of batteries. The chassis battery is a starting battery which is high output for a shorter time. The house batteries are normally lower output rate over a longer time period. I think the slide drew more current than the house system normally supplies in a short time period and that is why you got a low battery indication.

The tech was proper in switching it over as he wanted to ensure that you could get it in since you were having issues with your chassis battery. Once you get the starting/chassis battery issue solved then, and not before then, I would switch it back to the chassis system.