To tell you the truth, I'm totally shocked you got a 30 day warranty on this. There is no lemon law on used vehicles, only new ones and it takes multiple trips to the dealer for the exact same problem reoccurring to be able to return the car.
This site will tell you everything you need to know.
http://www.ag.state.mn.us/Consumer/C...Warranty%20Law
But basically, unless this Olds had less than 75k miles on it, the dealer was pretty nice in doing anything for you in this situation. To me, it simply sounds like the voltage regulator, most likely found inside the alternator.