Cobalt alt only charges sometimes....

I have a 2006 cobalt with the 2.2 ecotec, stock alt, but the vehicle only charges sometimes. Voltage will fluctuate between 12.4 and sometimes up to 15.2 while the engine is running (normally when charging it stays around it’s regulated 14.4-14.6). Not rapidly, just sometimes it’s charging then it’s like a switch is flipped and then it’s not then back to charging a while later and so on. Very frustrating because when it’s charging it keeps good voltage (13.7+) full tilt but when it stops charging I’m dipping to like 12.0-12.2. Question is, is this a fuel economy feature or a fault somewhere? It could be a faulty alt because I’m pretty sure it’s the original with 251k on it but I’d think if the alt was bad it would just not work at all, not sometimes work sometimes not. If this is some stupid feature that the car computer is controlling when charging occurs how do I bypass that??