We purchased a used travel trailer for a second unit to camp with our kids - We never had it hooked to a battery just to 120 and all worked both electric ( Microwave outlets , lights and refridg etc - but on our 4th outing plugged into a 120 outlet at a campground and slowly the lights got dimmer, our refrigerator stopped working ( all items that worked with both 12V and converter to 110 did not work) but anything that was Only electric still works (microwave, air-conditioner outlets) - - we checked fuses -including the converter all works fine . We thought about putting a battery in Just to check that but figured why did it work all those other times with out it ? anybody have any ideas?