I suggest Never disconnecting the Positive Battery Cable while a car is running ( Huge Spark) due to this is how sparks are created and batteries that may be leaking can explode.
The voltage regulator protects against voltage spikes, peakes. The proper way to test is this. Once the car is running, and at an idle, full battery charged or not, cautiously remove the Negative cable (way smaller Spark). If the engine dies the alternator has issues since it can't create enough electricity to keep the car running at an idle. If it keeps running the alternator is most likely fine and your battery has issues.
Rick