Battery boils over on 2001 Chevrolet Tahoe

I have changed the alt. and also the battery but the battery seems to boil over and there is corrosion all over the battery tray and surrounding area. What would cause the battery to BOIL over?

Asked by for the 2001 Chevrolet Tahoe
Sounds like the battery is overcharging. Overcharging is from a high charging voltage, caused by a bad voltage regulator in the alternator. Do you know the charging voltage while the engine is running?