Bad Alternator or Bad Battery?

[4.8isguy]

So I have had this issue lurking now for about 6 months now. There have been times where it doesn't come up for a month and then there are times it comes up daily. Start the car up. Fires up right away everything is fine. Maybe 30 minutes to and hour later my battery level drops significantly. it fluctuates between 9.3 volts to 11.6 volts. If I rev it good then it will go up to the 12's. Once it hits 12.5v all I need to do is shut the car off and turn it back on and its as if nothing happened and the car runs perfectly. This usually occurs when there is no spirited driving. Now everything leans me towards thinking its the alternator but about a month ago for a week straight almost daily the red battery symbol would pop up when I started the car and would go away within 10 seconds. Maybe its both but of course I would rather go with the cheaper option first. I've owned the car for about two years and have not changed the battery under my ownership. When I run the Carly APP the code I get is BDS-Generator 002E97. What are your thoughts?