@ludi you should check out Light Flow
. Also, since a lot of custom ROMs support different colors for notifications, I wouldn't be surprised if some already support a charging indicator. CM10 currently does not, but I'm sure you could ask for the feature to be implemented.
lonleyppl apparently beat me to the punch while I took my sweet time replying.
Heavy is good, heavy is reliable. If it doesn't work, you can always hit them with it.