The “X” makes your on-camera flash recycle about twice as fast as normal with any power setting or mode. Then the AA batteries will only do about half of the recycle work. That’s why the AA’s will last about twice as long as they normally would. You can use any style or brand of AA’s that you prefer but remember that they are still providing all of the power to the computer chips, display, power reflector and other low voltage features. The “X” simply assists in the high voltage recycle process to make it faster and more efficient for your flash’s AA’s. This also naturally lowers the heat produced by those batteries inside your flash unit helping to prevent overheating with the same rate of firing your flash. Of course, flashing it faster than you could without the “X”, will create more heat at the front of the flash.