Thanks for the replies.
I believe the Leaf battery is smaller than normal cars at about 40Ah. That still should be enough to power through a day at least.
I did some current measurements on the carloop. With the carloop only (photon removed) it pulls 2mA. When adding the photon that is connected to wifi it was about 37mA. I assume those are within normal expectations.
I did find a possible issue with my code that would prevent the photon from going to sleep. In the normal loop I was checking the battery and going to sleep if I had a value (GID) from the car. However it looks like the car, seemingly at will, will shut down the canbus which would prevent my program from getting that value so the power save would never trigger. I have commented out that check and will now do a powersave based only on the battery voltage.
The carloop.update() is at the beginning of the loop after I check if the wifi is still connected. I do see it going to sleep like it should during my testing.
One other thought - Is it possible the carloop is keeping the car computer alive when it would normal not be? I am not writing anything to the bus, the car spits out everything I need without asking. I haven't figured out why the can messages start and stop on the bus yet.