Garage Cabinets, Garage Storage, and Garage Organization

People, my mustang for 7 months I have been having problems. Up until now it has been running fine. January I replaced the alternator, and this week the battery. The battery & brake light flicker when I brake even after the new battery change. As far as I can tell I do not need brakes nor a battery. Could there be something draining my battery? Also, when I am at a stop light it seems to idle rough then once I accelerate it runs smooth again. This is something new. We have done tune ups and all of the usual maintenance ritually. Please help. I need my mustang to keep running