Another reason to drive old cars from the 1980s!
My keys have never ever even once needed a new battery. I have a key safe like this one mounted securely to the trailer hitch on my El Camino.
Pushbutton, Auto Mount W/Cover - Supra
It keeps the keys dry and safe. Only someone looking around under the car could see it and it would take a lot of time to remove it and get inside without the combination. I could not find a place to mount it on my 911.