Apple Maps is great, the only issue I have is that when I complete a navigation event, the map system appears to stay running on the actual iPhone and consumes a lot of power. If I leave my car turned off for even three or four hours with the phone not getting power because the car is off, the phone will be empty by the time I get back in the car.
If I plug in the phone after booting it for the first time and I never turn on navigation, it can stay without receiving power from the car for about 10 days. I can make phone calls or whatever, all from carplay, just not navigation. That's what kills the battery.
I was actually wondering if the my Chevrolet app was carplay ready, and therefore had its own map integration system which perhaps handle battery power differently. I guess that issue is moot since it does not even work within carplay as mention from Amber above.