I did a search for this information and didn't come up with anything - hope I can get some good opinions on this issue. I am going to have a Harman Accentra insert installed within the next week or so and plan on buying an inverter to back up the insert in case of a power failure. The Harman uses fairly complex computer-type ciruitry and, therefore, should I assume I need to invest in a pure sine wave inverter or would a modified sine wave inverter suffice? There is a considerable difference in cost. I already have a spare 12 volt battery although I may buy a marine battery depending on the rating of the spare battery I already own. Thats for any help. I assume I'll need an inverter capable of at least 500 watts, btw.