Alternator/generator/regulator problems of the 2006 Cadillac STS

After car had been immobile for a week, attempted to start and engine just clicked and car would not start. I placed the battery on charger without disconnecting from terminals, charge battery for approximately 10 hours. Tried to start vehicle again the next day. It started and I drove directly to an auto parts store (auto zone) and had them test my battery and alternator my system tested good, so I drove for a couple more days, this time I kept a close watch on the battery volts and they kept fluctuating up an down. I parked the car for another couple of days and the problem came back again. So I charged the battery again and then took it to a gm dealership and requested they troubleshoot it. They charged me 45. 00 and told me everything was good. Now I have the car at home again with a dead battery. I need to find a solution to this un safe problem. The car can shut off at anytime and I won't e able to restart w/o a jump. . Has there been other complaints similar to mine ? help help.