Thanks for the info on the 12v charger.
I'm currently powering my pi with this:
https://smile.amazon.com/gp/product/B01ASWX5PG/ref=oh_aui_search_asin_title?ie=UTF8&psc=1
Nice thing about this battery is that it fits comfortably in the console, and it allows pass-through charging. So when the car is sleeping, the pi runs off battery power. When the car isn't sleeping, it charges the battery while the pi continues to draw power from the battery. (for anyone wanting to do this, not all portable chargers allow pass-through charging, so if buying for this purpose, make sure the description says it allows pass-through)
Checked it this morning, and with the car sleeping most of the night, the pi used 12% battery. Which would give me a solid week of power if for some reason the car was asleep that long.