Battery light on dash

[AI85]

I just parked my 85' Carrera a few minutes ago after a short drive to work. Everything was working fine and it was the first time I have driven the car since last Wednesday. I parked it, and right when I turned the car off the battery light came on and will not turn off.
I started the car back up, everything was normal, I drove it around for a few minutes, parked it again and the light came on right away like before and will not turn off again.

So the car is sitting with the battery light on and I have no idea what it may be, Curious if you guys have some thoughts, any input would be great.

Thanks,

[Hugh R]

Check your voltage at the battery, if the alternator is working it should be putting out something like 13.5 volts DC, when turned off check again and see if the voltage is the same. Could be a weak battery or a dying alternator.

[DRACO A5OG]

+1 Alternator, but check the battery voltage too