I have a 98 Oldsmobile Aurora. Last week, I went out to the car and it wouldnt start. I jumped it, and it started, went to work, and had to jump it to get home. But the next day, it wouldnt start again. When I tried to jump, it would get the power with lights on in the car, but wouldnt start. I then took the battery out to be tested at Advanced Auto Parts, and they said it was the original battery from 11 12 years ago, and it was dead. So I bought a new one, and put it in my car, and it starts perfectly now. It has a 15 volt reading though on the onboard computer. I dont know if thats a problem or not. I have been talking with a family friend who works on cars in his spare time. He told me he knows that Auroras are notorious for bad alternators, and still thinks its an alternator problem. I dont wanna spend alot more money if I dont have to but wanted to get a more professional opinion. What should I be aware of or what should I be looking into?

Normal battery voltage, across the battery terminals, should be between
13 to 15.5 volts.
You should be aware that there is a battery thermistor attached to the
positive side of the battery terminal. It controls the voltage that the battery requires by monitoring the battery electrolyte temperature. If this thermistor
malfunctions (happened to me) the voltage could go too high, and would
lead you to think the voltage regulator was bad, which would not be the case.

I have 2 Auroras and my son has 1 and we have only had one bad alternator and my son caused that.
The other thing that kills batteries alot of times is the light problems. When the headlight switch starts having problems. You will be in the house and your parking lights keep coming on and going off. Its easy to fix and there are several previous posts on how to do it with contact cleaner.