Specialize: Protective Design-Included protect case which available to hold on the belt or bags; easy to carry. It's also much increased the protection. The connecting plug anti-wrong inserts design; avoid missed using to failureflashlight system. There included the srew which can hold on the tripod mount. Performance-Through the test, the sxternal battery pack can be able to reduce the recycling time. The recycling time is less than half of the original; also this is increased double times of flash as original. It is very suitable to use in continuous flash. Much useful-This product need to insert the 8new AA batteries(Same battery type as the flash unit) through difference connecting plug, support to use Canon, Nikon, Sony flash light, and greatly to increase the flash light working ability. This is the best for the professional person.