ORIGINAL: RC-FIEND
I can get a good 5 or 6 flights with only a slight drop in voltage...
Although this may not be why you are crashing, 6 flights with a 600Mah battery is impossible. I have a hanger 9 Digital Variable Load Voltmeter. The voltwatch is telling you the voltage when the servos are not under stress. (ie. not many Amps being drawn when plane is not in the air). On a 900Mah battery I could only get 3 flights on a trainer. Your plane is a sport plane and uses much more Amps to keep it flying because it isn't a floater. GL
I have flown my GB eagle 2 (a trainer)for 5 or 6 flights for 10 minutes at a time on the same type batteries (600Mah). I have done this many times without recharge. Also the plane was only on its 2nd flight after recharge before the crash. So I don't think the batteriey was the problem either...