ORIGINAL: Dr1Driver
7.2 would be the nominal voltage for a 5 cell pack. A NiCad is considered discharged at 1.1v, but will still operate the servos and RX for a while.
I could aways be incorrect, but I believe that for a 5 cell pack, you'd find that nominal voltage is 1.2 per cell or 6 volts not 7.2.