Seven servo's with one of them being a retract servo may be a bit much for your battery. I am also concerned about the 7.4 voltage. Most of the common servos are only rated for 6 volts max, hence the packs that came in the plane. Is the retract servo a true retract servo? If it is not, that could be a power drain. Retract servos shut off upon completion of a cycle and a standard servo continues to drain power, especially if the retracts are not set up correctly. Good luck...