I run a true sine wave inverter after I had some problems with the Coleman inverters. It was kind of pricey but it is a Samlex inverter and it will run both of my FE's for 24+ hours on two Sam's Club Type 31 Deep Cycle batteries. I used to get a strange sound from the fan on the Coleman inverter and the FE just seemed to run different. I no longer have that problem with the Samlex.
Mark