It doesn't look like the Caravan had unusual electrical problems (that area is 'average' on Consumer Reports). So I wouldn't hold your breath for the dealer to cover it. And your experience with the (aftermarket, I assume) warranty company is a good example of why those things are often much more trouble than they're worth. I would push the issue with them, the claim about the battery holder just sounds like an excuse, especially if no external damage to the cable can be seen. But now that your mechanic is into it, they might claim otherwise.