When you have 2 charges. If i use the first charge, the CD starts counting down, when i use the second, the CD keep going down, but once that hits 0 and i get a new charge, the CD will ALLWAYS be the full duration, making the 2nd charge useless, cause it just makes it a 1 charge button then.
Unlike the Earth, Wind and Fire charges of a monk, where the charges CD goes down independently.