Originally Posted by OhioYJ

Disconnecting the battery in any car with an alternator is a bad idea. Generators create power without power, alternators need power to create power. Disconnecting the battery can create power surges through the entire system. There are also vehicles that this "test" is not foolproof as disconnecting the battery will kill the vehicle even with a working alternator.

Generally it would be better to just measure the voltage at the battery with the car running. While I've come across alternators that put out voltage and no amperage this pretty rare. If the OP has a multi meter, this would be best. The battery sitting there should be, 12.2-12.8 if its charged (after it settles), while cranking / starting it shouldn't drop below 10.5 volts, and running the car should be over 14 volts but anywhere between 13.5-15 is fine. If you don't have a meter, most parts stores will test your battery and alternator for free.