Over the past few months I have been struggling to understand why (identical) test flights are lasting only 5-12 minutes (ave times overall are around 8 min) - with 8 separate tests used in this sample. I have a non-standard FC40, which I modified to use two externally mounted MadDog 11.1v 2700mAh 25C batteries, where I upgraded the props to the Phantom 2's (9") props, and I also installed a Walkera G-2D gimble. All tests have been done using dual batteries. I have two different balance-chargers. One that that came with the FC40 (the BC20-4). The other is a Thunder AC680 balance charger. Batteries are charged with the following settings.. Batteries charged on the Thunder charger are charged at 1.3A - typical charge time: <30min in a balanced charge. Batteries charged with DJI's BC20-4 charger are charged at 2A - typical (balanced) charge time: about 1 1/2 hrs. Using this method, I get an average of 8 min flight. NOTE: all flights are done by hovering the phantom at about 10ft, and holding that position until it self-lands. ALSO NOTE: that the Phantom is set to factory specs for all these tests. I'm posting this because it turns out I can get more flight time - averaging 18 min 20 sec - simply by charging both batteries used in a test with the DJI charger. But I found the Thunder charger (if used on one of the two batteries in a test) will fly for only half as long. I now know why flight durations were so short. Has anyone else compared these two chargers side-by-side? Has anyone else seen similar results? The Thunder charger is well liked in the RC community; that's why I got it in the first place; but these results have convinced me that the Thunder charger produces shorter flight times than DJI's charger. Yes, the DJI charger takes nearly three times as long to complete a balancing charge (and that is not so good), but for twice the flight time 'it is well worth the wait.