I have a 37 year old car. The (classic looking) Bluetooth radio is by far the most complicated electronics on board.
When I switch off the car, for safety, anti-theft and leaking, the battery is disconnected entirely with a key.
The radio looses everything: paired devices, position of radio tuner, volume, BT/aux/radio mode etc. Whenever you start the car, you'll need to mash at least five buttons and knobs to either find a radio station or reconnect Bluetooth. Modern tech is often so smart it becomes dumb again.
As I pointed out, some pieces and parts keep using electricity. Amongst which is the radio. This will drain the battery. Slowly, but surely. If I don't use the car in 14 days, it (probably) won't start; but with this wiring it does, just fine.
Which is why I installed a [don't know the english word]¹, so that my battery is switched off entirely. Everything in the car is fine with that. Except for this "modern radio".
Hiding that switch in a somewhat unexpected place also delays theft. 37 y/o cars are easy to steal; this makes it slightly less so.
Put a toggle switch somewhere in the cabin and splice it between the car radio power wires and the battery. So you can easily reboot the radio without having to mess around under the hood.
A push button normally closed momentary switch would be pretty slick too. Also it would probably be best to put it on the ground wire. Car radios will have at least two power wires, one for constant power (which keeps the clock set, and favourite stations programmed), and one switched accessory power to command it on.
Then again, a new $30 radio would be slicker still.
