What is a car data saver?

IT can be a device that keeps your car's computer powered while you perform a battery change. Newer cars have adaptive memory that would need to be re-learned otherwise. It also keeps your radio stations programmed and your clock time correct during a battery change. Another Device that it can be, is one that is plugged into your Diagnostic connector, to gather computer "data" and save it in hope for catching a glitch while driving for diagnostic purposes. Both are unrelated.