Giga factory has been announced, so making the batteries for Model 3 at scale will be a lock, as well. Apple uses a lot of batteries.
Apple could buy Tesla at 3x its market cap (the cost I believe they would need to hit), with a year of profits from their phone business.
Apple would need at least seven years to get a car on the road: three or four years to design it, followed by three to five years of building factories capable of any sort of modest capacity. Google is another likely buyer, but Google can’t compete with Apple’s war chest.