Welcome Bruce,
The x5 is rated as having a 20 hour runtime, it's not regulated so output will drop off over time.
Typically you can expect at least 10 hours of "good" output.
This thread may be of interest.
***EDIT***
Doh that Falcon's flying too fast for me /ubbthreads/images/graemlins/twak.gif /ubbthreads/images/graemlins/wink.gif