DFRobot Motor Controller

Hello to everyone.I have modified an RC car in order to work with Arduino UNO R3 and bluetooth(HC-05).It works very well but i have a problem with the power supply.I have 6 AA Rechargeable Batteries 2400mAh connected directly to Arduino power jack.My problem is that the car last only a few minutes.There is a way to last longer?Thanks in advance

My motor controller http://www.dfrobot.com/index.php?route=product/product&product_id=59#.VoFCR_mLS70