7 hours without power.....

[mike31154]

What size inverter do you have and what's the amp/hr rating of your car battery? If you car battery is rated at 100 amp/hr when fully charged, theoretically it can provide 1 amp for 100 hours. Knowing all your variables, you can figure out how many amps max the equipment you need requires and that should give you an idea if your car battery/inverter set up will last for 7 hours. If you can get your hands on a marine deep cycle battery, that's even better. They're designed to handle being fully discharged better than a car battery. I'd say two marine deep cycles will be more than enough.