98 lumina battery dies after a couple of days if

There may be a phantom load on the battery like a glove box, engine area, or trunk light that is not normally looked at. To check, charge the battery completely (overnight @ 4-8 amps), remove the negative battery connector and let the car sit. If the battery goes dead with all loads removed, then the battery has an internal short circuit and must be replaced. If the battery remains charged, then you need to find what is staying powered on when the car is turned off. You may have to start pulling each fuse one at a time to track this down! You will need to insert a low-current ammeter in series with the negative battery cable to tell when you have found the problem. BE SURE TO NOT TRY TO START THE CAR WITH THE AMMETER IN PLACE--IT WILL GO UP IN SMOKE!