Only 5 min flight? somethings wrong
Check the voltage on your batteries they should read 8.4v and make also check to see if they are well ballenced.
You also might want to check your blades. Bad blades will cause that kind of power loss.
Warped blade test
http://youtube.com/watch?v=_7PwNTXOWMs
Blade boil fix (boil for 5 minutes)
http://youtube.com/watch?v=RmNv8OlG6GQ