Totally agree with OzoneVibe here. I would never leave my drone etc, in a car or anywhere I am not for that matter… The weather is irrelevant, If I am not able to keep it with me at all times, just I I would expect to keep my wallet and other personal items with me, then I wouldn’t be taking it, plain and simple. Sure in the distant past, I have worked on sites, where security was of the highest level, where you wouldn’t get a second chance to explain why you were carrying a drone, but back then, even digital cameras and smartphones were non existent. but If that was the case and my job required me to work on a site, with such high security, it would never have left my house in the first place.
Yes while operating temperatures are quoted below freezing, just as with quoted flight times, they would be under ideal conditions, usually in laboratory conditions and very rarely do they test such things in the REAL world. However as for the battery taking ages to warm up… Oh they would soon warm up once fitted inside the drone and in flight, but yes the flight times will be reduced, just as anything with batteries has reduced efficiency at very low temps…
One thing to remember though, as with digital cameras. Taking a warm drone, out into low temp environments, you would need the drone to acclimatise to said low temps, before use, due to moisture build up, if you suddenly throw a battery into it and power it on, that moisture could mean the end of you drone.
So even if it was nice and warm in your car, but freezing outside and you spotted something amazing and thought, I must take the drone up and get some video or photos of this. You would need to take the drone out and let it sit in that much lower temperature fro a while, before using it, to eliminate the problems of moisture build up… Same goes for almost all electronic equipment, despite them saying it can operate down to -10 C whatever. If it suddenly comes from a nice warm 18-20 C interior, into a freezing -10C and you immediately power it up and start using it, there is every chance the moisture that builds up inside it, as it reacts to the temperature drop, could cause all kinds of problems. Even if it is something that is weather sealed, that moisture is going to build up