Low battery sign
 

Hi I wonder if u could help me.I have a o4 reg Audi a3 1.6 fsi. I am always getting the low battery sign I have bought a new alternator and a new battery and still have the same problem. Another problem I have got with it what I think is causing the low battery is when I put my window down all my dash lights radio,cluster start dimming then they go off when I do the window back up they dim back up and stay on still with the low battery sign.