Does not fight the opponent automatically but it still finishes the daily.

There is a if/else block in the doBattle function that starts with

if(currentPower >= battle_price)

Extract the code from the if block

// We have the power.
                battleButton.click();
                // Skip
                setTimeout(function(){$("#battle_middle button[rel='skip']").click();},1000);
                setTimeout(function(){$("#battle_end div[style*='display: block;'] .blue_text_button").click();},2500);

                if (sessionStorage.questRequirement === "battle") {
                    // Battle Done.
                    sessionStorage.questRequirement = "none";
                }

And paste it about the if/else block. Now just comment out the if/else block and auto arena will work fine.