flashing battery light

My 2001 golf tdi has a flashing battery light on the dash display while driving. The light is not consistent. It will flash for a few seconds and then disappear for a few minutes, only to start flashing again later.

My battery was dead this evening when I tried to start it. My question is what are all of the possible causes of an intermittent flashing battery light? thanks.

Not sure all the possible cause are listed anywhere, but off the top, I'd think alternator not putting out enough (replaceable regulator on it), old dying battery, corrosion in the cables...the usual stuff. Pleanty of threads on troubleshooting the charging system.
Helps to scan the car too!
http://forums.tdiclub.com/showthread.php?t=189479
http://forums.tdiclub.com/showthread.php?t=397932

Check the fuses on the top of the battery for starters; the one where the alternator cable attaches.