Voltage/alternator/Battery Problem

[felipe83]

My Sonic with 120K miles starts with a flickering dash problem, I took it to my local mechanic and he said the problem was the alternator, which needs to be replaced. The problem was replaced, it decreased notably but after a couple of months, with the A / C turned on, I began to notice that the air flow decreased for moments but it also felt as if the whole car stopped, all this for an instant.
I started monitoring the voltage through an OBD2 adapter on the control module and on the battery. Noting that when everything was normal the voltage of the control module was 13.7V and the battery was 12.8V. But when it went down in the control module it can go below 12V and in the battery near 11V.
Before I only felt with the car in IDLE now with the RPM above 2k the same happens
I took some captures showing RPM and voltages to get me across a bit better, and see if anyone can help me because it's kind of annoying.