MNTundra - thanks for all the info. There was nothing wrong with the old battery; I just upgraded from the cheap OEM house battery to three 230AH SLA batteries.
Your diagnosis sounds plausible from what I know now. If the solenoid is stuck, how can I get it unstuck? Can I just jump start the chassis battery and then retry the generator?
One other detail I forgot to mention. My main power switch has a light when it's powered on. Now the house won't power on, but when I flip the switch, it pauses a second or so and then the light slowly starts to turn on. A little dimmer than normal, and it doesn't turn off when I press it again. I disconnected the batteries when I saw that.
