2002 Chevy Astro Battery Light

First take the battery terminals off and clean them to make sure they are free of corrosion. Reconnect the battery and run the vehicle in park and check the voltage at the battery it should be between 13.7 and 14.4 volts. If the voltage was 10v and droping your alternator may be bad. If so, then remove the alternator and take to an autopart store that is able to test it. If it is bad replace alternator and be sure to charge the battery, an alternator is designed to maintain battery voltage and provide enough power to opperate the vehicle. It is not designed to recharge a battery.