To be fair, this is not something that non-nerdy car drivers should have to worry about. You should be able to park your car for months and not worry about it. You might need to put your car into a "super sleep" mode but it should last for months, and ideally you should not even have to do this change, it should notice.
Ideally the car would be designed with a very low power computer that can handle the basics of listening to the radio connection and noticing attempts to get into the car, upon which time it could wake up the main computer if needed. Frankly, it should not need to wake up the main computer for basic functions such as a brief status query, or detecting a keycard/fob. Such a device should draw only a few watts and be able to last many months.
However, if the carmaker did not include such a low power computer, it has another option. In super-sleep mode, it would wake up on a schedule, perhaps waking up less and less as time goes by until it's waking up only a few times a day. Your app would know the schedule, and tell you, "Sorry, if you want to remotely let somebody else in the car or do other complex things you will have to wait 30 minutes, unless you warn me in advance." You would be able to queue up requests to be done at the next wakeup.
If you park your car for a year you might have to wait many hours before you can wake it up. That's fine. Having to leave it plugged in during any long wait is a poor design.
