You have 4 options.
1. You can use "chip" called LM7806 to bring the voltage down to 6 volts. Or LM7805 to bring the voltage down to 5 volts. http://www.rctech.net/forum/showpost...postcount=1121
2. You can use diode in series from the battery.
3. You can connect the servo directly to the battery. NOT RECOMMENDED.
4. Buy another servo that uses less power.
Alternative to LM7805:
There is also a chip called LM309 in TO3 package. It has better voltage control than the LM7805 and can withstand more current. 7805 = 500 mA, LM309 = >1000 mA.
Then there is LM123 / LM323in TO-3 package = 3000 mA but minumum voltage for LM123 to work is 7.5 volts.