Janco External Flash Battery Pack for Canon 580EX, 580EX II, 550EX, 540EZ, MR-14EX, & MT-24EX Speedlite Flash Units (Replaces Canon CP-E4) External power source for higher flash capacity Replacement for: Canon CP-E4 Reduces recycle time by 60-75% Uses 8 AA-Size Lithium, Alkaline and Rechargeable Ni-MH or NiCd Batteries (not included)