One should be very careful to NOT EVER let your batteries drop below 12.0VDC or around 50% charge state when using high loads like the INVERTER when not on shore Power. If this happens and you don't immediately re-charge back to the 90% charge state before using the batteries again they will start losing their performance curve. Continuing doing this will most likely cause your batteries to be required to be replaced.
Those of us that camp off the power grid using our battery banks really watch this situation real close. Batteries don't come cheap...
Most INVERTER installs are directly connected to the battery terminals and if you have been running the INVERTER to power up things the batteries will start discharging. It really sounds like to me that your batteries are below 10.9VDC which is where my INVERTERS drops off line and alarms indicating low batteries...
Let us all know what you have found in your inspection of the batteries.
A fully charged battery without shore power on should indicate 12.5-6VDC. When you connect to Shore Power this DC Voltage at the Battery Terminals should jump to 13.6VDC or higher DC Voltage if the converter/charge has gone into smart BOOST mode starting to charge your batteries.
Roy Ken
