Looking for +12v while charging

I want to add ports to in my arm rest to charge my Nexus 7 and iPod (or what ever else I leave in the car) that are hot only when the EVSE is plugged in or the car is on. I'm not sure where to start looking for where to tap into that in the car. I think it would be a great to be able to keep devices charged up while not risking draining the 12v battery. Has anyone identified a circuit for this?

IMHO you wouldn't have to worry about draining the battery. The devices you mention won't have any effect on the 12 volt system of the car. The nexus 7 holds roughly 10 watts of energy. Thats a TINY fraction of the energy available in the cars 12 volt system. Even multiple devices wouldn't be a concern.

Even with my gas powered car I would charge devices without ever having any issue starting the car.