The easiest way I have found to farm Treasure Battles is to use Lucky Chloe and her move called "coffee grinder to scoot" which is performed by pressing
.
After the first hit connects, you can keep pressing
until you win as the move will loop.
Using just this move I have won over 50 battles in a row, and it also helped pop many other achievements like perfect victories, beating 10 higher-ranked opponents, and the various rank-ups all the way to Warrior.