My Review: If you use a Speedlite you already know you need an external battery pack to keep refresh times low. This Canon battery pack uses 8AA cells to augment the refresh rate of the flash. I use this pack in particular when I'm shooting the winners circle at a NASCAR event or shooting glamour where you don't have time to wait for the flash to cycle. You could certainly opt for a rechargeable system but the beauty of the Canon is that if you load it with Alkaline batteries it can be stored for years until you are ready to use it. In addition AA cells are available everywhere so if you do deplete the battery you don't have to wait hours to recharge.