In my car, I have to disconnect the battery when the cheap 30$ Chinese radio freezes.
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.
¹ here's an image: https://www.hsct.nl/wp-content/uploads/2014/10/IMG_8097-247x...
The yellow wire is named "constant" or "battery". The red wire is named "accessory" or "switched". The black wire is ground.
When the car is turned off, the red wire drops to 0V and the radio turns off. The yellow wire is supposed to remain at 12V to maintain memory state.
The yellow wire draws a very low amperage, and would take years to drain the battery.
Then again, a new $30 radio would be slicker still.
The radio drained my battery in 2 weeks, an absolute horror in Covid times when the car is in "long term storage".