Where do i even start in this (sorry in advance for the long book) Been having trouble with my 08 G37 for about a year now. I was having terrible misfire codes nonstop, i changed every sensor you can think of and new sparkplug and coils. I ended up getting a new entire engine with 55k miles off a 2013 370z. Everything was good for about 2-3 weeks and on the highway it random shut off and completely lost 100% power. No cranking, no interior power. no nothing. I had it towed back the next day to the place where i got my engine swapped. but unfortunately my car got stolen after being there for two weeks and also no work was done. Luckily i found it and is back in my possession since i had an apple air tag and again got it towed back to my house. They completely destroyed my key fob on the door (which is how they got in) I wanted to see if i could get any type of power so i connected battery cables from my truck to my G, Which made all the power come back on and now the car doesn’t recognize my key. which makes me believe they reprogrammed a new key and booted mine off. I was posting this to see if anyone had any ideas on why the car turned off on me and lost all of its power and also wanted to see if i need to reprogram my key.

Heres the trouble maker

 

That's, uhhh, a lot going on there, hoss. I'd probably start with the factory service manual section on Security Control System and work diagnostics from there. Maybe it's as simple as getting the key to recommunicate with the ECM.
https://www.nicoclub.com/service-man...2013%2FSEC.pdf

 

100% with @digital.aaron , getting the keys reporgrammed would be a great first step.
If you still have engine problems after that, then suggest getting with whoever did the engine swap.

And dang, these cars are getting stolen a lot more frequently lately.