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 an extra 10% so about 83 amps. To power for 5 hours you'd need about 400 amp hours, which is a fairly big battery bank. But, if you wire your system to supply some of those amps from your running motors, you can reduce the size accordingly (for example, if your motors can supply 30 amps, then you only need about 250 amp hours of battery capacity). Note that lithium batteries can be fully depleted, but Lead Acid / AGM batteries should only be run down to 20%-50%, so those battery banks have to be even bigger.