I connected this inverter to 4 group 29 marine batteries in my trailer. I have 5000 and 13500 BTU AC units. It fed a 13,500 BTU unit on a 100 degree day for 1.5 hours before the batteries died. I started my generator hooked up to just a 100 amp charger. The AC unit then continued to operate normally on the inverter. It powered the 5000 BTU unit all night without a generator, and in the mornings I brewed coffee in my Keurig coffeepot. My batteries were still 12 volts. Worked great.