Can battery testers at advance auto be wrong?

Go to more than one car place to have it checked, For instance Auto Zone and NAPA.

Nope usually not.

And I just saw what car you drove, congratulations, you're going to need to change your alternator OFTEN!

I owned a 1997 Saturn SC2 coupe for 9 years and had to change my alternator out 7 TIMES!

It's something about their belt ratio and alternator speeds that just wear them out, that and their really horrible build for them. I'm not completely sure, but I can safely say, please, oh please, PLEASE, start looking into a different car if you can... Owning my saturn was a NIGHTMARE. I moved onto a Honda and have been rather pleased, the honda is even older than the 97 Saturn which is funny.

Even GM admitted that Saturn 'was a failed experiment'

I also bought a 1983 Datsun 280zx after I canned my crappy Saturn. I LOVE that car! It may be old, but I learned to be a mechanic with that car, it's now completely restored.

MORE DETAILS:

If its a 2002 SC2, even worse, the production quality began to drop sharply after 2000 (Not like it could drop any farther than it already was).

The Saturn ION was rated one of the top WORST cars of all time due to its horrendously poor engineering.

Here's the link, it made #5! http://www.latimes.com/business/autos/la-fi-top-te...

Also:

Check to see if you have any power on in the vehicle, a good place to check is to see if your glove compartment box stays lit when the drawer is closed, any sources that could drain the battery. For me, I once had a computer issue (Which too was replaced) with the car that drained my battery.

Try to tighten the battery cables as lose you can crank the car but it will not start because of the voltage drop during cranking the computer will not function.