So recently my voltage has been dropping to 12.6 and it stays there until I stop. When I start the car up and for the first bit driving the voltage stays from 14.5 to 14.2. But it always just drops to 12.6 out of nowhere whether I have music on or not and stays there. I have a battery in the back, big 3 in the front, stock alt and stock battery under the hood. Any help is appreciated.