[s-cars] Battery Charge Light?

[Cody Payne]

Over the past 6 weeks I have seen my battery light come on my 92'
generally at idle.  It goes away shortly after getting the RPM above 2K
and only happens about once every 2 weeks or so.  The alternator is
original however the brushes were replaced about a year ago.  Battery is
about 18 months old (Ultima Red Top)

Does this warning mean that the alternator is not producing enough
voltage sporadically at low RPM's?

Thx

Cody