Adding another line/wire in metal conduit
You need to determine first as asked in the comments, do you NEED a neutral?
That would depend on the car requirements. Refer to the car manufacturer's manual.
The power supply is just dumb power.  All the fancy charging logic circuitry is in the car.

NEC chapter 625 has specs for the charging system. Note it has to be GFCI, possibly AFCI too, depending on where it's installed.
Free code lookup here-
https://www.nfpa.org/NEC/About-the-NEC/Explore-the-2017-NEC?openpage=106&amp;access=open
(free registration required)
unfortunately without search function- Chapter 9, tables 4 and 5 have your answers about conduit fill.  

Chatty explanation here-
http://www.codebookcity.com/codearticles/nec/conduitfill.htm