When you attack battlegrounds you might be tempted to finish one after the other.
Don't do it but try something different.
Each BG has a fixed strength. You can attack with just 1 of your troops 100 times or send 100 troops at once.
The result will be the same. You just chip away on the number of enemies in the BG. Enemy troops don't recover in their strength.
Now, don't finish off BGs in your attacks. Just attack until only 1 yellow line is left and until it says "few" or "weak".
Do that wit all BGs that you can access.
Then wait until a PvP or BG quest (ideal if both are at the same time) and finish off all the BGs you have already weakend earlier.
That time you can finish off a lot of BGs with few troops and little time and reap multiple awards (the BG award, PvP and/or quest reward).
To attack BGs use troops that are cheap and fast to produce such as dwarfs, paladins, knights, nomads, etc.