Converter Causing Generator Surge

All the replies suggesting a problem with gas or eco switch or anything relating to the generators aren't paying attention. I too, have two generators, one almost new and the other several years old. Both respond in exactly the same way. Startup in the morning and either generator runs high from the start, then begins to econo but instead surges gently back and forth UNTIL I throw the switch and disconnect the batteries. Without the batteries charging, either generator purrs along perfectly while running anything connected onboard but, reconnect the batteries and the same thing recurs. I have cleaned all the contact points on or near the batteries and have topped up distilled water (although they didn't need much if any). I can't wait very long for a reply as this needs to be addressed shortly. Has anyone come up with a solution?