Xbee Power Consumption

Hi all!
Does any one use Xbee, a product from Digi? I an using some Xbee modules to build a WSN. Unfortunately, It seemed dropping voltage very fast. Do u know how to improving power consumption of xbee?

PS: I have read Xbee data sheet and it received "To improve low power current consumption, the XBee should set a couple of unused IO lines as output low. This can be done during application initialization as shown below." But I don't know how must i do?

they are very low power consuming devices

I mean that how I can config xbee to get long battery life, may be using GPIO PIN. Because, a few day ago, I tested a module Xbee with 3V supply but it seemed slow down voltage very fast. So, if I config it as Xbee end device mode, It loss power very fast...