My son has a 2017 fav 4 push no start..

First of all disconnecting the battery can and will cause electronic problems requiring a dealer to "Flash" the system. This sounds like a security system intervention, have you done the reset listed in the owners manual? If you have and still no results then it may already need to Flashed to bring it back online.

No security system. Just immobilizer. In which case would be crank no start.

It a 2017 it has a security system. Check the owners manual.

This is exactly how a really dead battery behaves, like one with a dead cell or two. You get little lights lit up, but not enough juice to even make the starter motor wince. That's also why the car's telling you to put it in park. It thinks the shift mechanism isn't allowing electricity to get to the starter. Replace the battery and pray that that battery-disconnect you did didn't trip the security system.

When I answered this question, I got the message, Answer will be posted shortly..... I remember years ago when this site used to get more questions in a day than it now gets in a week or two. It's CarGurus inane management of this Questions site that's now keeping people from coming here to get help. When answers are given, they're not posted for days or at all. And now newcomers get frustrated with all this mismanagement and leave... I suggest CarGurus either GIVE A DAMN or cancel this Questions page all together. It really has become useless.