Alternator or battery issue?

Hey guys, yesterday I noticed my battery light came on for a brief moment during cruising. I got home and did some tests on the battery and alternator. The readings are...

Battery: 11.9v

Alternator output at idle: 11.7v - 12v

Alternator output at 2k RPM: 13.6v - 14.1v

I disconnected the battery and charged it with my portable charger to 12.5v. The next day I drove the car for about 45 minutes doing some errands. Came home and checked the battery voltage and it was about 11.9 volts again. Seems like the battery isn't holding a charge but could that be due to the fact that the alternator output at idle is so low? Hmmm

A few notes...I have a Steeda underdrive pulley that came with the Steeda belt drive system for my Whipple. Car has been running fine ever since the Steeda parts were installed 5 yrs ago. I just can't remember if the alternator output was this low at idle before. Optima Redtop battery is 2 years and 4 months old.

Maybe it's time for me to upgrade to a 200 amp alternator.