Unwinnable battles in general remind me of puzzles in adventure games that are completely random (ie, no way to actually logically figure them out). There is NOTHING so annoying as thinking you have a problem set before you that you're supposed to solve, and then realizing that there's either no way to solve it, or the only way to "solve" it is stupid trial and error and 50 re-loads. Sure, I've put up with it/done it to get through an otherwise good game, but I don't find it fun.
I don't have to win a fight to get through a goal - perhaps you may finally realize if you can't win the fight, that the solution is you have to somehow sneak by/trick the baddie instead of defeat/kill him to move on - kind of like getting by Humfrey's moat defenses in the Xanth novel series - but fighting the same battle/reloading for a couple hours before realizing or being told by the game that it was supposed to be unwinnable and there's no other solution would really tick me off. Waste of time I don't really have anymore.