Well, from what I'm reading you want to winch with the engine off? Even with two batteries that won't last but maybe 20 or 30 feet of pulling, if that to be honest. You'll have to run the engine no matter what. with two good batteries and no isolator you won't have a problem with starting. You'll have to stop the winch to cool down long before you will be able to drain both batteries. Warn doesn't seem to publish a duty cycle on their winches but I'd venture to say it's some where around 5 to 10 percent at 100% load (i.e. 1st layer on the drum). To answer your question, I believe, you will need to run your engine no matter what when winching. No you will not need an isolator, you'll be fine with two batteries.