Auto Zone does not have the equipment to properly test high output alternators, I dont care what they tell you. They cannot simulate actual conditions that the alternator will be used for under different rpms and different loads. I have a good friend who works at one of our local auto zones and I took him a high output alternator to see what it showed on his tester. It was a 250 amp alternator and was only showing 210 amps on their tester. I was showing 248 amps on my bench tester. This was another companies alternator too, not one that I built. I recommend getting a high output alternator from a reputable company that you can trust, that is your best bet.