Depends on what the battle is going to be like. If we're in with a decent chance of winning, then I'd go with Princes of the Universe [http://www.youtube.com/watch?v=RnrXiaPVeHY] by Queen. There are few better songs to get you pumped for something like that.
On the other hand, if we're clearly outnumbered and outmatched, and are almost certainly going to die, then it's got to be Who Wants To Live Forever [http://www.youtube.com/watch?v=OgK_keIJq-4], also by Queen. If you're going to die, you might as well accept it and get on with what you have to do.