Originally Posted by Marvin the Martian
If it has become one solid color, and it doesn't appear to be filling up, then it's full. I don't think mine ever turned green. You can also check in System Settings-->Info and find the battery percentage there.
In my CZ it is also white but quits it's flashing/"battery filling up" animation. When the animation is stopped it should be charged 100%. That seems to be the same basic graphic (no animation) Sandisk has used on all of their players for years.