RE: Coleman Generator
I think you have already received the right answer:  The modified sine wave
coming out of the generator is not liked by your charger.
A brief look what I could find seems to indicate that (if you have the
generator I think you do) it has a special connection for charging
batteries.  If so, did you try that connection?
BTW, I have such a 'battery charging' connection for my Honda and it works
fine tied directly to a battery.  But it is slow compared to using my
charger that is hardwired to the 110v system in the van.