It's not bad, just remember. Remove the negative first, then the positive, then Connect positive first, then negative. This way you will not make sparks.
Most of the time, yes, it depends on how long the battery was removed for. Your radio will have an internal memory powered by an internal battery that will store memory for a while, even without a battery in the car.
There is more memory that you can lose when disconnecting the battery than just radio presets. You can lose codes and other computer information having to do with engine performance. I have heard people report that their car idle and throttle response was effected for a while after changing battery. They make something called a memory saver that will supply 12 volts to the computer while you change the battery. Or you can hook up 12 volts of power to battery cables and leave on while you are changing battery. Just an FYI. I’m going to be doing that today lol.
