Does the engine alternator charge house batteries?

Thanks. Your answer makes sense. I will verify tomorrow.

I had a scare today, driving this RV at night and seeing voltmeter gauge at 12.1, I thought that the alternator was not working (as happened on my semi truck the other week).

It turned out that everything was fine, but the voltage gauge on the dash was fed from the same wire (circuit) supplying headlights, and suffered from voltage drop as headlights were turned on. The batteries see nice and healthy 13.5 volts.