Hi,
You need to simply measure the current drawn from the 6AA battery pack. Use a typical multimeter.
Divide the Ma/H rating of the AA batteries to find the number of hours it will run...
Other: IF the power supply, like the switchMode supply on the YourDuino RoboRED, draws less current from the 6AA's than the Arduino draws, you will get more time... For that kind of possibility see
THIS page..