Not sure if this is by design or not: I bought a Canon CP-E4 external battery pack for my 580EX II when it's in slave mode for umbrella shooting. When the flash is mounted in the hot shoe of my camera, it uses the external battery pack and recycle times are greatly reduced. However, when I place the flash on a light stand in a softbox, the flash simply will not utililize the external battery pack. I've tried ETTL and manual modes, still no dice. I've tried setting the internal flash settings to use either "internal & external power source" and "external power source", still same results. I'm I doing something wrong? Seems kind of pointless to always have to strap the large external battery to your camera to use it. Also defeats the whole "off camera flash" approach.
