I have a 95 gt that I have built from the ground up, built the whole motor. During this time I relocated the battery to the back. Since the build I'm having trouble with my battery/ charging system. The battery and alternator are new and have been tested and work fine. The grounds are checked and good. My issue is I can charge the battery completely on a charger, put it in the car and start the car and the battery will drain fast. If I run it for like 15-20 mins the car will lose all the battery and will shut off and won't start again. Can anyone help me with the issue and where I should look. I checked fuses as well and all are good.