Help! Truck on side of road. Voltage steadily dropped to 7.5 volts and died

[Redland1]

03’ 9900i with 04 cm870.Voltage steadily dropped and around 8.5 the stop engine light came on so I pulled over.Let it idle since it’s 17 degrees here and it died when it got to 7.5 volts.Don’t know if this has anything to do with it but a couple of days ago I replace the radiator and water pump so I had to take off the alternator.Once I put everything back together and started the truck I could hear the belt squealing and tried belt conditioner spray but it got worse and finally went away half an hour or so before the truck died.I checked the connections on the alternator while it was still running and also the battery connections and everything looked good.What could it be