HEY we just got a 2017 Hyundai Elantra and it does the same thing as Neenus G, of Innisfil,ON,Canada if it sits over the weekend its hard really hard to start???when we got the car the battery was dead dealer ship put new battery in we are back to the dealer ship with this they dont know why???really strange ours is a button start no key just a fob somebody has to know whats going on.
If this car was sold to you with factory warranty intact, you could try a different dealership. You can also elevate the problem to corporate, instructions on doing that should be in your owners manual.
You May have to leave it for several days so the dealership can see what it is doing after sitting for several days without being driven.
Is your car parked close enough to where you keep your keys that the fob can communicate with the car?
That can keep the cars systems on because it thinks you are close enough to want to start the car. If so. keep your keys inside a metal box or as far away from the car as possible.