Some sort of battery issue !!!???
 

What’s up guys I have a 2011 370Z that I just changed the alternator and battery on. Car has been running smooth for 1 month since change with the exception of the battery gauge going from 14V down to 11V sometimes while car is running. Battery actually died on me today. Which brings me here. When I move my windows I see the voltage fluctuate. I know something is not right I just don’t know what? Any ideas?

Try checking:

1. What’s potentially draining your battery (anything running/drawing current even when car is off).
2. Check the alternator, as this is what keeps your battery charged when driving.

get a new battery

What type of Alternator? (used, rebuilt, aftermarket?)
What battery brand?

Did you do the install yourself?

Either way, that's the last thing that was done. I'd check with loose connections or shorted wires.

something is draining power, happened to me and turns out it was a aftermarket viper alarm system that was constantly draining my battery. I too replaced battery and alternator thinking it was going to fix it.