Always rule out parts problems first.
While replacing the battery, you may have damaged the flex cable for the front camera and sensor (which includes the microphone). Did you completely disconnect the screen to replace the battery or did you leave it connected?
So I would double check the condition of the flex to insure it doesn’t have any tears. If it looks fine and it appeared to be well connected, then you could [guide|50592|try a replacement flex]. If that doesn’t work, then you may have a logic board issue.