I currently have two GPS nav apps that work off of my contact list and today Google is updating their app to download maps to use sans data which I will be installing shortly. Update:I downloaded the latest app and the max area to download is 31x31 miles. Not large enough for me.Having used OnStar for navigation, i can tell you that i am not impressed by it at all. It is very easy interface to work with but the main meat and bone of it is bad.
Talk to human to find/navigate to a address
1. No re-route.
2. Arrival is approximate. e.g, One of the place i wanted was on a state hwy intersection. Once we reached the intersection, it said arrived. This is NJ, it is not that easy. Luckily i knew the area.
About using smartphones for navigation, sounds good at first, but i would rather have it as a last minute. Battery and data charges are not worth it.
Leaves us with just 2 options. 1. In car systems and 2. Garmins of the world. I prefer Garmin as we can get up-to-date maps for free vs buying expensive In car systems with costly map updates.
As far as battery goes, I have my phone charging via the 12v plug..