Bad battery or bad alternator?

Hello everyone.
The problem that I am having is that I cannot tell if my vehicle is suffering from an alternator or a battery problem. I own a 01 GMC Jimmy 4.3.
What happened was this: As I was pulling out of a parking space, my battery light went on, and my car just stalled. The lights were still on, so I put the car into park, and then everything went out. I couldn't get my key out of the ignition, the lights wouldn't turn on, and I couldn't put the truck into any other gear. Then I got out, popped the hood, and put the support up. Once I did that, then the lights went back on. I went back into the car, put the key in the ignition, and attemped to turn the car on. The lights went on, the starter kicked, but the car wouldn't turn on. After a couple of minutes, the car then turned on, and I drove home.
I also checked this morning, and when I put my foot on the gas, the interior lights begin to flicker faster and faster. Also, there is a squeeking sound on he engine, probably coming from the alternator.
Now, what do you think could be the problem? Alternator or battery?
Also, I had the air conditioner on when this happened, so maybe that was a factor as well?
Any help would be greatly appreciated!

you might have 2 different problems. When the alternator light comes on on the dash, that is almost always a bad alternator.

But from your discription of lights flickering on and off, that could be either a bad connection at the battery terminals, or at the other end of the battery cables, or an internal break in the battery.

Alright. Well I dont know if my car has an alternator light, but I havent seen it. The battery light was on when this happened, even though it is a new battery.

Now, where should I lokk for the "other end of the battery cables", and what do you mean by an "internal break in the battery"? Im not really knowledgeable when it comes to cars. :frown:

the battery light is the alternator light. It comes on when the system senses no output from the alternator.

Also check the connectors from the alternator to the battery. If you have a multimeter you can check the voltages when revving the engine.

Or if you do not want to do this yourself bring it to a shop and ask them to perform a "load test on the battery" and if that comes back in check then have them do the same thing for the alternator. But make sure when they do the one on the alternator they turn on the High beams, rear defroster, and the air conditioning. So the maximum load on the alternator is being excerted then it should tell you.