370 Z dead battery

I have a 2011 Nissan 370Z, base, 6 speed stick, just over 7k miles.
On Saturday I washed the car, then took a short drive and put the car away unlocked.
On Sunday morning the driver’s door was locked, nothing responded to anything. The battery was completely dead.
I charged the battery for a couple hours and the car started normally and ran fine the rest of the day and every day since.
The dealer checked everything and found no problem.
No, I didn’t leave the lights on…they would go off automatically anyway.
Anyone have an idea?

Zero voltage? Did u put meter on battery to check voltage when it was “dead”?

Did the dealer check for a parasitic drain?

+1 for mountainbike. Something drained your battery.