I agree with 67Dart273. Unhooking the battery cable on a running car can cause a voltage spike that can blow out everything electrical on a car. Search "load dump" on Google and you can see how serious a problem it is. Modern alternators have Zener or avalanche type diodes that will absorb these spikes in case a battery cable comes loose or is removed while the alternator is charging. This is also one reason to update to a late model alternator if you are upgrading the electronics on your car.
