I have a cellular game cam . I am running it on 12 AA batteries . I just got a 12 v battery / solar charger unit . Do I need to remove the AA batteries to run that unit ?

Depends on the camera. The manual should state as such.

As an example, my RidgeTec originally wasn't supposed to have internal batteries installed if running on solar. After a firmware update, the company now recommends running the interior batteries as a back-up should the solar system fail.

Check your manual or call the company.