I was driving my Camaro home and stopped somewhere and turned the car off the car was driving good and fine and when I go back to turn it on it starts ticking while I’m trying to crank and just starts draining the battery. Any idea where I could look cause my brother in law hooked up a jump box and it drained his jump box when he hooked it up to the battery and battery instantly died. I had the battery tested couple days ago and was told the battery was good. Thanks in advanced for suggestions

 

alternator may be failing, bad diode can drain battery although I have not seen one drain so fast.