Flickering AC lights on battery

[wfeffer]

I have a 96' Tourmaster that we bought about a year ago. When be purchased it, it had 4 new house batteries (lead acid) 2 new engine batteries, a Xantrex Freedom SW 2012 inverter charger and 4 solar panels that are so old they do little more than keep the house batteries topped off. Since we purchased it I've never run any AC appliances or lights off of the batteries till recently and I noticed that the lights flicker and any AC device powers on and off. All of the DC lights work fine. I have a decent understanding of home electrical systems but there are so many components in an RV that I'm not sure what the most likely culprit is here. My guess is the inverter/charger, but it's also one of the newer items in the RV so I'm not sure I should blame that.

Does anybody have any suggestions on what might be the cause or how best to trace the issue? The RV has a battery tender full time and has been plugged into shore power for a year with no issues while plugged in.