First off, I really like this Q45. Of all the cars I have owned, it is one of the nicest. This issue happened on a road trip from Las Vegas to Reno and I didn't have a voltage meter. I first smelled the battery when I stopped about a hour from Fernley. Had to fill a boiled dry battery with bottled water and get a jump start. When I got to a auto zone in fernley, I borrowed a meter and realized I was getting 17 volts. When I called the mechanic that changed the alternator, he told me to unplug the clip with 2 wires from the back of the alternator and I could drive it for 50 minutes or so but would eventually have to plug it back to recharge the battery. So, I unplugged it and finished the hour drive to Reno where I bought a Meter. To my surprise, it was still getting 17 volts. At this point everything electrical still worked and it was about 4:00 pm. I drove the car to a Goodyear garage where the boss guy had a look. He removed some fuses and unplugged the 2 clip-in wires from the + side of the battery in a effort to bring the voltage down. The voltage was still at 17, so I made a 12 o'clock appointment at a nearby pep boys for the next afternoon to have the alternator changed. It was at the pep boys that evening when the drivers window and seat adjustment stopped working.
The next morning at 8am, I called the Infinity of Reno dealership and asked to be stand-by for their mechanic. I drove it to the dealership, but they got slammed so I had to drive it back to the pep boys for the 12:00 appointment.
The alternator was replaced and I was now getting 14 volts max. I changed a handful of burned fuses. The airbag fuse wouldn't hold and kept burning. When I started it, I got the "Transmission Malfunction" on my trip odometer screen. I put it in drive and started back home because the transmission was working fine. Other than the drivers window and seat adjustment not working, blowing the airbag fuse and the window relay going "click" and dropping the voltage every 10 seconds, it ran and drove 100% great. When I got home, I removed fuses until the relay under the dash stopped clicking. The "power Window" fuse made it stop clicking, so I assume it's the power window relay.
I got home and didn't drive it for 2 days. I researched the "Transmission Malfunction" diagnostic using the trip odometer lever turned counterclockwise as the key is turned on while the transmission is in Drive. I started and drove the car until the temp gauge was in the middle, parked in a shady spot and did the transmission diagnostic. The trip odometer went to AT CHECK and stayed there for 5 minutes without displaying any codes or messages. Thinking the test failed, I turned the key off and put it in park. I tried to start it, but it would barely fire and stalled out quickly. Very weak. I grabbed a gas can thinking maybe it ran short on fuel, but it still won't start. I had it towed home.
So far, I checked all of the fuses, but not the relays yet. I took the gas line off at the injector pipe and and checked, the fuel pump seems to be working fine. It just won't start.
Could I have damaged something by trying to do the transmission test? I know the system getting 17 volts for a few hours can't be good.
My next step is to either call a mobile mechanic or have it towed to Nissan or another garage to have it diagnosed and fixed. I will probably wait for a week to see if I can figure it out, but I'm not confident I can figure it out, even though I have always worked on my own vehicles.
Any suggestions? Like I said, I really like this car a lot and it typically runs great. 20 mpg on the highway and it will do 140 mph easy. I have had it to 120 and there was plenty of room left.
Thank you all for any help you can provide.

to NICO!

...so much here to wade through. The transmission diagnostic wouldn't cause your issue.

Where are you located?

To get started, I'd post a rundown of all of the fuses that are burnt out and relays that are unplugged. With that said, from what you describe, you really need professional help. If you can find a technician with some old Q experience, that's who you want. Get your wallet ready