A quick end-of-season follow up to this voltage issue.
Once I joined the accessory battery to the bank of 4 inverter batteries, the voltage issues went away. Essitially, it made the 2 'banks' into one larger bank. The engine control system seems to like that . . . So, I left it alone.
Solves 2 issues . . .
I now have 3 battery banks instead of 4, matching FET isolator of the solar charging system.
Voltage warnings have gone.
Here's to hope for next season
