Correction, connecting 2 batteries in series to increase voltage does not increase AHr. Therefore, two 6 volt batteries @ 225 AHr connected for 12 volts is still 225 AHR. .... 6 batteries wired for 12 volt results in equivalent three 12 volt batteries @ 225 AHr.

redoing the calcs:

3 batteries @225 AHr =675 AHr

Inverter: 8000 watt @ 120 volt (output)= 800 watt @ 12 volt (input) = 66.67 amps ... (Is 8000 watts the calculated load? Has efficiency losses been included?)

service time: 675 AHr / 66.67 amps = 10.12 hr

Efficiencies of the system was neglected, so I think your actual operating time will be about 6 to 7 1/2 hours (at full load), 60% to 75% efficiency of inverter, wiring, & motors.

Note efficiency of the battery is accounted for in its AHr rating. Which is 20 hours of 100% loading or approx. 80% of battery capacity. ... The above system will be depleted at 10.12 hours (80% discharge), At which time the batteries needs recharging.

*** my 2 cents and exercise for myself to understand.

<message edited by edwmax on Wed, 09/5/12 6:45 AM>