An inverter cost about $100rd per watt, and if you use a good one they have battery low voltage protection which will keep your batteries from going too low. I don't recomend more then 4 six volt batteries on a 24 volt inverter. I also have my house wired so that big draw units are pluged into the grid, washer, dryer, frig, water heater,and the rest of the house on inverter. The frig is protected ,pluged into, a Avtek Protek/c. What this does when the power comes on it checks the voltage and also waits about 5 min. before passing thru the currant, in that way the frig dosen't get spiked when the elec comes on. I also have gallon jugs of water in the frig and freezer, making it a true ice box when the elec is off. A full frig stays colder longer, so fill it with water as you empty other food stuffs out.