Here's the rough math: 8.1 amps of 110 Volts AC is about 900 Watts. So you'll need a minimum 1,000 Watt inverter. If your inverter were 100% efficient you would need 75 amps of 12 Volts DC to power a 900 Watt device. (900 divided by 12), but inverters are only about 90% efficient so you'll need...