The previous posts have really answered the question, and that answer is, "It depends."
You will have to do some research on your tow vehicle set-up to know if a "back feed" is possible. Even if it is, it will be a long, slow process as the charge, in both directions, is just a trickle. IMO, in an emergency like you describe, a good set of jumper cables connected to the trailer batteries will get you started.
Larry, Eileen, and Finley
2004 Alpine 36FDDS
Third motor home, first Alpine, no need for another.