a battle is an event, you should lose a movement point for every event, spells included, so players would have to make tactical choices, as it is, you place your best army in the middle of any number of enemies and destroy them all and you are still able to move
I would put things even further : any battle takes out one movement point from the pool of an army, for example you are attacked during the AI turn, for every attack you lose a point of action, as a result next turn you can't move
this tactic would allow a king to escape a much faster army by sacrificing some units to slow down a pursuing stronger army
