generator stalls when converter tries to charge battery

Thanks for all the responses. I DID run a portable car battery charger from the Yamaha generator to charge the battery directly and it did fine! The battery was new a few months ago. With the battery disconnected and the Yamaha connected, I can run all AC and 12 volt appliances no problem. So, I'm not suspecting the generator. It is only when I have the battery hooked up that the generator stalls when I turn on the WF-8955PEC converter.