In the search for longer flight times, I bought some of the CF battery trays that attach to the side of the Phantom and gave then a try. I found that two batteries barely gave me two extra minutes of flight time....I believe that this configuration puts the batteries out to far and the props are actually pushing down on them, creating drag that is seriously affecting the flight times. Looking for another way to do this, I realized that the two trays when joined at the middle exactly fits in the grooves between the landing gear on the Phantom and can be easily secured by zip ties. The pictures I uploaded ( I hope ) will show what it looks like. After getting things secured, I tried a flight with two MadDog 2700 batteries which yielded 21 minutes of excellent flight....very stable and it hovered like it was tethered in place. The second flight was with a Hunger 5000 battery which gave me 17 1/2 minutes of time with the flight characteristics the same as the two battery flight. The two MD batteries weigh 403 grams and the single 5000 weighed 406 ....the only other thing on the FC-40 beside the stock camera is a GPS tracker that weighs 55 grams so the weight was almost identical. I am very pleased with the times I got and the mod for the tray to hold the batteries was very simple. I hope this gives some other fliers ideas on how to improve things with little changes and share with the rest of us.