ORIGINAL: MTK
I drove mine hard one time when I flew a fifth full flight once last year(95 min + of flying that day), with a starting voltage at 7.55 or so. After the flight, voltage had dropped to 6.2. Revived the battery okay but that told me to never do that again. So now, 75 minutes of flying session is all I do. Ending voltage is consistently around 7.5V
What I didn't mention is that an average 20min flight drops my 2S airborne lipo voltage about 0.2 V, starting with a full charge. After about 75 minutes of flying pattern style (not 3D which would draw more), my airborne has dropped to about 7.5-7.6V.
Point is that one should exercize caution when the lipo voltage drops to around its rated voltage of 7.4.....there is point where the voltage drops like a stone.