Why I have Brake and Battety lights on my Sonata 1999? they pop up together than dissappear than they on ogain. I have them on an off all the time. It happens usually when i accelerate my car. MY mechanic cant find breason. My battery is good and brakes good too. No any problems when driving.

 

Did you check to make sure the brake lights are working ok?

 

I once worked on a new Tibby with a smaller a/marker performance battery that was doing the same thing. All it was is that the battery was simply to small. Your issue might be your alternator not putting out at higher rpms and loads. Or you have one of these batterys.