Just for fun reach down to the alternator pulley tomorrow morning. Grab on to the cooling fins just behind the pulley itself. Can you turn the pulley by hand? I assume you may have already checked this.

On occasion if loose the belt will not squeel. But alternator output will be substandard. You should never be able to turn that pully by hand. Remember
the transfer of several horsepower to the alternator are required at full alternator output.

Also try not to lock yourself out again this evening. If my wife and myself were your parents we might be then discussing how safe it was to let you out. Or I would be asking the wife if you were really one of mine.

All kidding aside it is nice to see you helping out your dad. I think you will get to the bottom of this pretty fast.