Red light indicator Battery

I have a 1996 S420 (W140) that had the red battery indicator on the dash light up for about 5 minutes. I thought that that indicator meant that the alternator was bad...but checking the voltage it's at 14.1 - 14.3 with many of the cars lighting and accessories turned on. The battery is indicating just above 12 volts when the car is shut down.
My question is, why would the indicator light come on for only a few minutes? is it a battery going bad? or is it an alternator going bad?
Any ideas...