Hector said it earlier, that 9V battery can be used, but it's not especially good idea, since they got fairly small capasity. That means, you will get short operating time before you need to change battery.
I recommend 5 or 6 AA-batteries or rechargeable AA-batteries (For example eneloops). Or the LiPo battery Hector linked. They will last much, much longer.
9V Batteries are about 100-150mAh (milliAmpere hours, means how much electrical energy they hold.) Wich is really small capasity compared to 2200mAh LiPo-battery or 2000-3000mAh rechargeable batteries.