C152
The voltage regulator in the alternator might be failing or perhaps the external drive belt. Either way, you were losing the alternator. You will then slowly run down the battery, the radios will fade, and finally your flaps won't work. You can turn the master off and run the plane just fine, saving the battery. Beware of partially functioning flaps, they might not go to 30 degrees and they won't come back up if the battery is too weak.
You made the right decision in quitting the flight.