I've had issues with my batteries. I read that checking with a multimeter would help diagnose problems. I found that my batteries were toast and repleaced them. I read that generator should register around 13 volts at the batteries. Mine read around 4 volts. Any suggestions about how to continue the investigation?

You're running the TT on a generator but the batteries aren't being charged? If that's the case then I would guess that the 12v converter is probably bad.

Not sure how it could read 4vdc with the batteries connected.

Batteries were disconnected for reading.

It sounds like the converter. Have you checked the output directly from generator (with meter) ?

Measure with the batteries connected and generator running. It should read around 13.8vdc give or take. Like others said, could be the converter/charger.

I'd also test the output from your converter/inverter, had that issue before myself.

Also, not sure what type battery you're using, but deep cycles work far better and reliably and, always keep an eye on the water level if charged/plugged in a lot and keep distilled water on hand to keep the cells at level.

You have a bad inverter. If you are putting the test leads on the battery cable when they are disconnected. Possible it could be low output from the genny feeding the inverter but far less likely.

Are you sure that the batteries are connected correctly?
For them to read 4V there must be a dead short somewhere.

Disconnect the batteries and measure battery voltage while unhooked. Let me know.

I replaced the batteries. They read 4 or 5 volts prior to replacement. They were 4+ years old.

This may sound really basic, but make sure your inverter is plugged in. The inverter for my old Fleetwood plugged into an A/C outlet right next to it. Somehow the plug came out and eventually my battery died from using the overhead lights. Replacement inverter's aren't that expensive and are pretty easy to install.

Go ahead and measure the off line battery voltage of the new batteries. Please.

Up date ?

I found the voltage at the batteries is 12.09.

Is that with the generator running or with batteries disconnected ?

Generator not running. It seemed like the generator was actually pulling the batteries down based on watching the battery status inside the trailer.

The resolution was to replace the convertor. I am back in business. Replacing the convertor was not a fun task. It wasn't as simple as the YouTube video showed.