I have been having on going issues with my 09 G37X Coupe.

The initial issue started with a dead battery. I jumped started the vehicle and it ran normally. A few hours it died again and I assumed it was a dead battery and replaced the battery. The car started without an issue. Several hours later I tried to get into my car but it was completely dead. It didn't detect the smart key, none of the lights came on, and it nothing happened when I pressed the start button.

I got the car towed to a dealership and they diagnosed a dead BCM. I get the BCM replaced and everything runs normally for a week.
The issue now is that the car will completely die randomly. I will park, get out of my car do an errand and come back to the car. I open the door sit in the driver seat and when I press the start button the whole car dies. It doesn't detect the smart key, the ignition start button won't work, the light on the transmission shifter doesn't work. All the electronic components of my car basically dies.

The only fix I have found so far is disconnecting the negative battery terminal.

Has anyone else experienced something similar? Any ideas what the issue could be?

 

Has it rained since the issue started? Have you check your sunroof drains?

 

It has rained several times but the problem also occurs in dry conditions.

I checked the sunroof drain today and it was not blocked. Have any other ideas?

 

Can you check the ground from the negative battery terminal?