How long should batteries last

[wrapperman]

I am trying to see how long my battery bank should last. On a fully charged battery bank I disconnect the shore power and run off just the batteries. With 2 fantastic fans running , the inverter for the refrigerator and any other parasitic load I then let it sit for 8 hours. After that I check the voltage and the reading is 12.24 volts with the loads still on.
My question is, what is considered 50% charge (voltage at the terminals) for these conditions? Fans running and inverter on.
My rig is the 378

[clr]

The voltage for 50% of capacity is 12.10 Volts. But the voltage will be lower when you read the voltage under the load that you are talking about here. If you disconnect the loads and let the battery sit for a few minutes that is when you should measure the battery voltage.

[wrapperman]

Thanks
Your answer is what I was looking for.