Dragline, I am going to change the front battery. What I want to know is why is the teg going to the front battery instead of the back one which is for starting?
front battery needs power to control the intelligent systems. If it's flat the car's brain is basically dead and it won't start with a fully charged rear battery.
If the rear battery is flat the brain (powered by front) will know this and use the front battery to start the car.