Change the alt.
the belt is worn and loose change the belt and tension properly
Problem is most likely your alternator or your fuel pumps.
Most likely it will not be the alternator. It sounds as though the alternator is working very well. It will be a faulty battery or a battery drain due to something left on or shorted out. Usually a boot light or glovebox light or recently fitted stereo.
It's probably the belt slipping. Check for belt tension. When an engine first starts the alternator works harder to recharge the battery. During that time, the alternator is harder to turn and if the belt isn't tight enough there can be some slipping between the belt and the pulley.
The battery "starts" the car...after that the alternator keeps the battery charged. They work together in other words.
Take to a mechanic ASAP
When the engine first starts, the alternator puts out a little extra current to recharge the battery. If the tensioner pulley is a little loose, the belt will slip on the alternator, making a terrible sound. Check/replace the tensioner. The spring is probably loose.
Alternator, air conditioner.
Axle or alternator .
An ac bypass pulley for a 1989 Chevrolet can be purchased at any auto parts store. The cost for the pulley starts at $26.04.
The alternator.
It sounds like your alternator is no longer recharging your battery. You probably need a new alternator.