I have a 2005 S40 and the battery indicator light will flash.  It will be in the middle or green range then it will shoot all the way to the max and then down to nothing and then back and forth one or sometimes a few times.  Just wondering what could be the problem a short of something more serious I bought the bike used and do not have a owners manual.  I was hoping some one has any suggestions cause it drives me nuts when driving at night. I tried to search but nothing came up so if there are any links please let me know.

I don't think it's standard issue on any of the years.

You probably have a loose connection somewhere which will cause brownouts and surges in voltage when reconnected.

its an after market volt meter...how many leds ???
mine has 8 from left to right 2 each red amber green red left of green is under volt right is over volt(charge)
when i first turn on the key second amber is on(head lamp draw)when bike is running at 2 green but as rpms change second gren winks in and out at wot only one green ..
if you have the single led type volt (battery) meter and it shows green you should be ok
the three led type red amber green a operate the same...
doesnt hurt to check for loose connections  me thinks your meter is rpm sensetive...