1999 Pontiac Sunbird battery issue

Hello, If the battery is down, take it off to get it checked and recharged. Some of the national brand autostores will check it for free. You shouldn't use the alternator to charge a down battery. When the vehicle is running, it is the alternator that supplies the electricals, not the battery, as long as the charging system is ok.

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 80 ° F will discharge 25 amps until the battery drops below 10.5 volts. That number is probably stamped on the battery somewhere.