1991 Chevy Lumina battery kees dying

Welcome to the forum. If you have a digital multimeter you can do some checking. Place the leads across the battery posts, the generic specs for a fully charged battery is 12.6 volts. Do that test with everything turned off, take a second reading across the battery posts, engine running. The second reading should be higher than the first, if it isn't faulty alternator or wiring circuit.

Another issue is a battery drain, maybe a light left on somewhere, engine compartment--trunk--interior somewhere. Best time to check for a light is in total darkness. You can check for amp draw, probably 30 to 50 ma max, that is nowhere close to half amp.