Some real-world battery life results for Arduino projects and XBee mesh networking radios have been published. Use them to help choose which battery setup is right for your project.
All tests have been performed at room temperature with nominally fresh or fully charged batteries. Tests with multiple run times are intended to give a sense of the potential for variance in the results. Results were monitored in a program that keeps track of the first and last time it receives bytes on the serial port.
The results are available here.