Just a note that not all batterys are rated for fast charging. If the batterys are not rated for it, the batterys will overheat and the life will be severly shortened. I tested the safe flight times on 40 sized trainers and found that the receiver batterys were good for 7 to 8 flights with 500 or 600 mah batterys. On sport planes or larger heavier planes it was down to 6 flights. My original receiver batterys have recently started to go down hill so I switched to 1500 mah Lithium batterys. Now the flights don't make a dent in the plane batterys so the limiting factor now is how long the transmitter batterys last which is about 2 hours "on" time. I plan on changing these also.