The Battle Field setup is a very fun addition to the game. PvP is an integral part of keeping the game fun and entertaining. At first empires battled fiercely to control the Battle Fields. However, it has become apparent which empires will win the arenas. Many empires are not even bothering to contest the regions anymore since the winner is almost certain.
There is no incentive for most empires to try to contest the Battle Field anymore given the proven likelihood of losing. No empire wants to waste their time for a loss and the empire-wide morale decline associated with the defeat. I suggest that you a reward chest at the Battle Field NPC. He would give each soldier or citizen member of an empire that entered the Battle Field a chest for participating.
The Battle Field Chest would have randome loot similar to the Scroll of Chance. However, they also have a chance to get some good items. The chance increases depending on the % win the empire gained in the Battle Field Event. Items would include chance for the epic items that normally are only given to the Emperor of the winning empire like the new mounts or King Certificates. I think this feature would renew interest and competition in the Battle Field, especially once a fee to enter is added.