9.6 volts is way too much......you didn't mention capacity......how many servos, analog, or digital.......the capacity of a battery you're going to use depends on the load you're going to put on it.....if your going to use 8 or 9 high torque digital servos then you want 6 volt 3200mAh battery...actually a li-ion battery and a regualtor would be best.
But if your using 5 analog standard servo then a 4.8 volt Nicad 600mAh battery, would do.
Remember batteries in series and voltage is additive, current remain the same....batteries in parallel voltage remains the same but current is additive....or in other words more capacity and longer charge times.......