Hi All, As with many F550 pilots, we experiment with different battery combos to gain the maximum flight times. I also have been playing around and just about 20 minutes ago landed my 550 after an 18m43s flight with two ReadyMadeRC 4200mah batteries in parallel. The test flight was a controlled flight taken under near identical conditions of a test flight with just one of these batteries. Each battery weighs 292 grams giving my F550 a total lift off weight of 2152 grams (2.152 kgs). The original test flight with one battery gave me 10m 42s flight time. Both test flights were undertaken in conditions where the wind speed was under 2.5 kph (ranging from dead still to very light breeze) Both flight tests involved 50% hovering, 25% moving forward/sideways and 25% climbing or descending. As far as I can see, the addition of the second battery has been a great success and now gives me the confidence to use the 550 for some filming in areas where its stability out-shines my P2, whereas previously the P2's flight times made it the preferential machine to use, despite its comparative 'twitchiness'