i either need a new battery or alternator, but i dont know which. i need to charge the car to start it and the charge doesnt last for long. someone told me if i disconnect the negative terminal on the battery while the car was running and it kept running it meant the battery was bad. it kept running, but im not a hundred percent on it. the car hasnt been used much lately but the problem was there when it was in use. so which one is it?

 

Take them both out and take them in to get checked. AutoZone will check them both for free.

The reason the person told you what they did is that if the alternator was bad and the car was running off the battery, disconnecting the battery while the car was running would cause the car to die. I've never tried this theory so I can't say if it is a good test or not.

I would just take them in to get checked for free.

 

the alternater test works. but so does going to napa and getting ur battery checked fr free lol