Yeah, looks like a remanufactured unit is $400.
I really don't know how old the battery is since I have only had the car since the end of September. And never looked at it too closely to see if it has a date code on it.
I was just leafing through the maintenance manuals for the car and see that GM considers the battery voltage to be acceptable if it is between 8.3 and 16.5 voltes (or thereabouts). So far I haven't found any indication that a fluctuation while driving of 2 to 3 volts is considered normal or not.
But it does seem to me that we had a similar situation with our Chevy Astro van where the voltage was fluctuating quite a bit. Then the alternator died.
Darn, I hate like hell to have to put it in the shop again so soon. But I'm going to be nervous taking it on a trip anywhere. I'll bet getting a tow truck hooked up to the Z is not going to be an easy task, and no telling what experience level the guy in the truck will have. Sigh.......