Since our lock is motor driven the more force the motor has to apply to rotate the bolt the more battery is expended. This can be caused by warping of the door due to moisture, temperature or by an obstruction in the path of the motion of the bolt. A rough path can dramatically reduce the battery life. You might also check to insure the wire that runs between the two lock pieces does not interfere with the tailpiece this can also cause the motor to work a lot harder to turn the bolt. The solution is to make certain the motion of the bolt is very smooth.
Special Note: Do not attempt to solve this problem by installing LI AA batteries. These batteries can often damage the electronics in products and with a 'load' are often much higher than 1.5v each. Best batteries to use are 1.5v alkalines.