What I meant was when you come to a stop or slow right down do the headlights dim. Its not if the camera affects the lights Rather the car affecting the camera.
The only thing that will cause it to turn off is either a bad connection or low voltage.
If it was mine I would get a long bit of wire and attach it direct to the + terminal of the battery and see what happens.
Despite the dealer saying the battery is Ok I would say it isnt or else the alternator is not charging it enough.
If it still does it when you run it like that, the last method is to put it in another car and see if it does it
If not there is something wrong with the charging circuit in your car or its the fuses you have it connected to