Battery won't hold a charge on 98 chevy astro van? Starts, runs, but next day won't start again. Had a rebuilt alternator put on 6 months ago

Check the battery first.....charge the battery with a battery charger and reinstall it in the car..then check the amps on the meter in the car...leave the battery in the car overnight (don't run it) and check it again in the morning..if it drops you have either a short or the batterys dead.