I would say you do not need to replace your battery. Your complaint is a noisy bearing, not zero output. Your altinator may continue to work for yrs, mnths,weeks, or hours. Just can't tell. But unless you have an engine light on, your altinator is working. If you have a gauge on your dash, or a multimeter check for 14+ volts across your battery while the engine is running. If you do than great. Altinator is putting out, but your still left with the unknown of when will it die.
I bought a LIfe Time Warranty altinator from Autozone about 4 yrs ago. I just had to replace it again couple days ago. That was when I noticed my AC compressor issue. I got a new $130 altinator from Autozone under warranty even though I couldn't find the reciept. They had me in the computer. What a deal!
I would recommend getting a new Altinator from a parts store that will give you a life time warranty.