Thanks Harry. I'll bet that's what the problem is.

I asked Vanner how to test the isolator. I told them what Liberty told me, that the battery is charged from the alternator. They said to check voltage on the battery side and compare to the other side when the engine is running to see if alternator current is passing through. There should be a -.4V to -.7V or so difference.

I checked it with the engine NOT running and surprise, surprise ... battery side was 10V and the other side was 13.5V. Checked the 12V alternator and it reads 13.5V. I know the 12V alternator charges the house batteries, and the house batteries are at 13.5V, so there must be a connection to the house batteries through the alternator, and the isolator must be an isolation between the house batteries and the generator battery.

If the isolator was working, I would think there would be a similar voltage on both posts. The isolator failure must have happened months ago and that caused the new generator battery to get used up. Since it is at 10V, I'd guess it's all used up and wouldn't take a charge if the isolator is replaced.

Does any of this make sense or am I imagining things?