I hope someone has an answer to my vexing situation. I bought an AODELAN External Flash Battery Pack Battery Power Bank for my Canon speedlight 580EXII hoping to see an improvement in recycle times. Off the camera with 12 Eneloop Pro AA batteries charged up and plugged in to the flash unit with 4 Eneloop Pro AA batteries in it, less than 1 second cycle time with full flash test button...every time. Turn everything off and connect the flash unit to the hot shoe of 5D MkIV and switch all back on again.....4 seconds recycle, same as if the high voltage pack was not connected. Apparantly the high voltage from the pack goes straight to the capacitor when flash occurs so why the 4 second recycle on camera?
