1. TD-381 is a power pack for Canon flashgun . 2. TD-381 uses a dual circuit charging system. Charging time is much fast than any other battery pack. 3. Convenient design; you can either use 4 or 8 AA batteries. It will be faster recharged when using 8 AA batteries. 4. TD-381 uses a new charging method, its save more than 25% power compared with original power pack. It also can be used with difference types of battery. 5. Compatible flash: Canon 580EXⅡ,EX580,EX550,MR-14EX,MT-24EX。