my car's battery will die after it is running for a little and then wont start back up(batter dies)

also i just pulled out the alternator without checking and put another one in and it didnt help,but this one i checked,if i disconnect the battery the car dies,and i know thats a sign of a bad alternator but is there anything else that could cause this?????i checked the fuse and its good,checked the battery fuse and its good

 

fixed