Is there a way of recovering car memory(radio,time) after forgetting to use a memory saver?
The memory used to store the radio stations is volatile, and once the battery is removed, the data is gone.
May be, some radios have a power buffer to keep the data for a short period, or they have non-volatile memory. But in this case, the stations would just be there, and you don't have to recover them somehow.
For the clock, it's the same.