Any part can be defective even a new part. They are made by man therefore mistakes can and are made in their construction. Just be thankful it failed while the car was under warranty.
Because alternators eventually wear out - just like most other car parts !
It may be that you need a new alternator.
First start the car then pull off the positive on the battery if the car dies than you need a new alternator if the car keeps running u may need a new battery. A word of caution, testing an alternator that way can cause damage to the alternator. The alternator needs power to make power unlike the old generators from the past.
you need the alternator to charge the battery with no alternator when the battery drops to about 10 volts car will not run at all.
Your alternator is probably not keeping the battery charged while the car is running. You need a new alternator!!
That would be a good thing because putting the belt on after you start the car would be dangerous.
The car may need a new alternator.
A new battery or one that tested good is in the vehicle and the car is still losing power. the alternator is what charges the battery while the vehicle is operating.
if your car will not stay charged, try running radio lights and all sorts of things that plug in to ac plug and if your car dies you need a new alternator
Car would either have to be running or alternator removed for bench test
When the alternator goes bad or goes out completely, the car's battery will be drained. I suggest you pull the alternator and have it tested. If the alternator is bad, you will most likely need a new battery as well. The cost is around $200.00.
More likely the bearings in your alternator wearing out. Get a new alternator.