Hello! The power of Battlegrounds doesn't change. Try to minimize your losses by analyzing the Balur's Units on a Battleground before raiding it. Check the Unit Defensive stats. Choose the type of Units that will be the most successfull against Balur's forces. Remember that Cavalry Units may be the strongest ones, but they're not always the best type of Units to send at a Battleground.

I totally agree with Aline,  The power of Battlegrounds doesn't change. Try to minimize your losses by analyzing the Balur's Units on a Battleground before raiding it.  

-edited (removed links) by Gandalf