You really have a simple mind. The alternator does not "put the same voltage on the battery to charge it".
The regulator applies the maximum voltage from the alternator (after rectification) to the car battery and regulates the charging current. The car battery will accept the charging current and the internal chemistry in the car battery makes the car battery terminal voltage rise. The regulator is supposed to cut off the charging current when the car battery terminal voltage reaches a point that the regulator considers the car battery fully charged.
Please try to put this into your head: A charger must be a voltage much higher than the battery voltage. The charger is supposed to limit the charging current to a safe level for the battery so that the battery would not overheat or cause internal damage. Fast charging with excessive current will cause damage to the battery in the long run. Avoid fast charging the battery if you are not in a hurry. And avoid overcharging. Overcharging a 12V car battery will boil off the water in the electrolyte. Fast charging a lithium battery with excessive current or overcharging a lithium battery will cause bulging, and eventually battery fire.