I know I may be stretching the term battle theme a bit far here, but my nr.1 favorite battle-type song is probably from
Power Rangers Zeo: Battle Racers on the SNES, music by Hiroyuki Iwatsuki & Haruo Ohashi (track
Enemies Town).
http://www.youtube.com/watch?v=EcH0Vg4EG3Y
Closely followed by the much loved
Mystic Ark (track
Now, Full of Power, I'm Your Opponent!) and
Mystic Quest (track
Battle 1). Then a wealth of others but these 3 are probably at the top.