whats going on is his amp is drawing to much voltage like pioneer said. his electrical system cannont keep up with supplying that much current. when it cannont keep up with the much current his amp doesnt get the proper voltage needed and it goes into protect mode or shuts off until the car's electrical system can catch back up. if i were you i would tell him to read up on the big 3, or you could do it, it is on a sticky in the electrical and wiring section at the top of the page, and do that to his car. it should solve all his problems. and i would do the big 3 before he gets a new battery, and it is alot cheaper.