Hello, I am making an geocache reverse box based on this project Overview | Reverse Geocache Box | Adafruit Learning System.
I use an GPS module, a LCD, 4 Buttons and a servo motor.
I already programed almost of the code i need but now i have some problems in who i will power the all circuit.
When i was doing some tests with the GPS module i founded one problem. I used 6 AA batteries to power the Arduino i notice that the refresh rate of the GPS was very slow. I thought that was a codes error but when i made the some test with the Arduino powered by the USB of my MacBookPro i notice that the refresh rate was the one i was looking for.
The batteries i used was 6 rechargeable AA batteries but i thing they were already a bit exhausted. Is that the problem? i did not have time to try it with full charge ones, will it make a lot of difference?
Anyway, i searched very much on web to find an alternative solution for power the arduino, but when i found answers i found some questions too.
one of the possibilities i have founded is to buy an usb battery pack like this one:
http://viewitem.eim.ebay.pt/AA-USB-Emergency-Portable-Mobile-Phone-iPhone-4-5-Battery-Pack-Backup-Charger/321082101820/item
Is it possible to power the Arduino with this? Is that more efficient that power the Arduino with 6 AA like i have done?
Another possibility is to use a Lithium Ion Polymer Battery (like this: Lithium Ion Polymer Battery - 3.7v 2500mAh : ID 328 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits), but i think is a little expensive and the mAh is less than a 2 AA batteries. And it will be better to use AA batteries because they are easy to change and a lot of common.
What is the best solution for me?
Thanks in advance,
Miguel Moita
I used 6 AA batteries to power the Arduino
6 batteries will give you 9V.How much current does your circuit demands?
Thanks for the reply.
Vinda de um português como eu! 
I do not have any way to measure the current for now. But maybe it is essential to conclude what is the best solution for me, right? I only be able to know in two about weeks. 
HugoPT:
I used 6 AA batteries to power the Arduino
6 batteries will give you 9V.
Only for a short time. After that it will drop down to about 7.5 (for about 80% of the battery life).