My buddy has a 2001 XJ 4.0. He told me that he went outside to start it, heard a pop, and nothing would happen. The starter doesn't even click over. My multimeter reads the battery as having 12 volts, but whenever he turns on anything (head lights, interior lights, start the jeep) the battery drops to almost zero. The head lights will come on for a second, then fade away. Once he removes the "load" the battery goes back up to 12.4 volts. I checked the auto shut down relay, and it is in working condition. All of his fuses are okay. I didn't have much time to help, so I figured I would ask if anyone knows what is wrong. Thanks.