It should be a 600 watt inverter with a 1200 watt peak. I have an inverter air conditioner with a variable speed/capacity compressor which makes it VERY efficient. At low levels, Kill-A-Watt never exceeds 312W. The compressor self-test and slow-start takes approximately 5 minutes. The battery side voltage never drops below 13.2. The battery is full and at 13.8 with no load on the inverter. At 312 Watts per Kill-A-Watt (AC side), the inverter will lose power, turn red and alarm. For me it's basically useless if I lose 1/4 of the nominal load.