Battery capacity - 8 lithium 100Ah 12V so about 9000+ watts. Fully charged in the evening 13.5V on the panel. The only consumers are the fridge and freezer, that jointly use 85 watts so by the morning 700 watts have been used and I should have 8300wats of power left but the voltage is now 13.0V -
You mean about 9kWh.
You can't use voltage on a lithium battery as a means of estimating state of charge, they have a different discharge curve to Lead Acid.
You will have whatever capacity is left after use, remembering to add losses for the inverter/charger overheads and self-consumption.
