Your alternator may be dead. Volts while running with lights on should be around 13.8 - 14.2 volts. Anything more or less means a dud regulator. Was it squealing when the volts were 14.7 or 12? usually when the alternator dies temporarily, the car runs off the battery, then if it starts charging again squeals because it puts a big load on your engine which makes the belt slip a bit. Then as the battery charges again, the squealing stops. I would quickly get the alternator checked before your battery goes flat and the car just stops dead! Was the battery light on?