You should be careful about overcharging. About 6 years ago, I went flying one weekend, left town for the week, and my dad charged my batteries for the next weekend. He forgot to discharge my reciever battery, and just plugged it in. Since batteries charge at a higher rate than what they are rated for(4.8v packs need 6v input to charge, and 9.6v packs need 12v to charge), the batteries can hold way more power than they should. Well back to the story, I went flying that weekend, and lost a plane. upon inspection of the wreckage, I noticed that the switch harness had melted the shielding on the wires between the battery and reciever. The wires shorted and caused the controls to lock up, and send my easy sport in a full speed death spiral straight into the dirt. My advice would be to run the batteries down then charge them for the 12-14 hours reccommended by the radio maunfacturer.