Welcome to CHR! No intention to offend with a basic question, but have you cleaned the battery cable connecting surfaces? I've seen several alternators and batteries replaced when all that was needed was to clean the oxidation from the terminals for a good, sound electrical connection. Lights pulling down the battery says that either the alternator internal regulator is bad, the alternator itself is bad, or the path for the power to get to the battery is blocked or high resistance. A good auto parts guy should be able to pinpoint this problem in about five minutes with some test gear once all connections are clean and tight.