why does the battery light comes on at random whilst driving lasts for about 20 - 30 miles

barry, April 2009

I have known brake fluid reservoirs on 206's to leak. On some models the reservoir is situated above the alternator. The leaking fluid plays havoc with the alternator and can result in it being necessary to replace not only the reservoir, but also the alternator too.
Worth checking, and if this has happened with yours get the reservoir changed now before the alternator is ruined. They are not cheap.

Chicks Fan, April 2009

also check the plug on the back of the alternater that can cause the light to come on clean with a bit of wd40

ricky, April 2009

Usually this is a sign that the alternator is starting to fail...

John, April 2009