2006 impala ls

Charge your battery so that the car will start. Get a test light and check for power at the big wire at the alternator. If no power. You possibly could have a bad fuse or fusible link to that wire. If good with power the unplug the connector at alternator and check for power at one of those wires. One or more should have power. If no power then maybe bad fuse some were. It have power you will need to full Field your alternator when motor is running. I'd after full fielding it and still not charging battery then I am guessing your new alternator is not working or not installed correctly. You should have around 14 volts at battery when motor is running. If you can load the alternator up to get the volts down to 12 you should have maybe 90amps

I had my car checked 4 times even down to the battery wires being replaced

Then I am not sure with out looking at it myself. If the battery is not getting charge by the alternator then something is not right with the charging system. It's not that hard to figure it out. Their are not a lot is parts to it. I mean it could be something crazy like the crank pulley bad but in all my years I have only seen one car have that going bad to make the alternator not charge the battery. But in the case the battery light was not on. It could be the PCM or the BCM. But if you have had it at a shop and they could not get it right then I would say to take it to the dealer or a better shop

I no you said it has a new alternator but take back off and have tested I have seen new parts out of the box be bad.