It probably has to be something with either the belt or the pulley. I had the same problem with another car about a week ago. Well, it was
fixed a week ago but the problem was long than that.
Whenever I started the car I'd get a squeak and the volts would dip. Whenever I pulled up to a stop light I'd get a squeak and the volts would dip. When the volts dipped the lights also dimmed. You see, the belt was slipping so much that I wasn't getting any charge from the alternator and was solely using battery power. When I started the drive the squeak would get louder and louder until I could hear the belt catch the pulley with a chirp and the volts would shoot up to the normal range and the lights would brighten. Lucky the problem was just a loose belt.
It sounds like a belt or pulley because you are still getting a charge from the alternator, right? The problem comes into play because of the squeak and the squeak is because for some reason the belt is slipping or grinding or SOMETHING!! If you are keen on this date, I'd just make sure the belt is good and secure and hope that it doesn't squeak so you can at least get through the night (or morning
), then you can be free to take a more thorough look tomorrow.