I dont even think you would have to worry about the heater.....just the Power head....the temp. shouldnt drop that much

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.

well i grabed a 2hp 1000w gennie to day at crappy tire. it was just under 100 and was $80 off. this should allow me to run heaters and PH's. on three tanks. now all i need is for someone to housit for a day. o kidding i have a roomate but heis moving at the end of the monthe and im sure if he is willing to stick around for the day as he is the most selfish person i know. one of the many reasons hes moving on.

PS today is the last day for this sale .