question

Does that mean if I don't see the lights during the warning flash period, that there's no way to tell what the error is? How long does it flash before it goes to a solid warning light? I had tried turning it off and back on, but it didn't go through a flashing light phase, just went straight to the solid light.

You were right on the cause. I turned the AC off, turned the battery connection on, turned the AC back on and it started charging the battery normally. Its on the default setting (configured for a gel cell as I understand it) but those specs don't look like they should cause a problem for my lithium battery. I was just going to leave it off until I was able to correctly program the charging.

Am I correct that I can't just split the incoming AC so it also leads to the AC breaker panel? I'm assuming some kind of undesirable feedback would occur with the inverter output since it goes to that same panel.

It would seem like a desirable modification to make the inverter/chargers not completely control the shore power. My previous inverter/charger from decades ago did not do this. I understand the benefit of being able to boost poor shore power, but the present setup still seems undesirable (unless a simple T of the incoming aC line indeed works fine).

One odd thing (to me) is that my Multiplus had been connected the same way with the battery cutoff for at least two weeks before it apparently decided this was wrong and threw the error.