[Mario_Marques]

Originally Posted by njlou

Hi The concept of shutting down the alternator does have merit.
Forgive me if it has been covered before, but the latest models of BMW have a sophisticated computer controlled system which cuts off the alternator if the battery charge is above 80% and puts it on when the car is coasting or the brakes applied, or if the charge goes below 80%. The alternator provides (some) drag to slow the car and at the same time charges the battery.
Think of it as a mini regen system.
There is no reason you couldnt do it manually. Like a switch on the brake and another one elsewhere?????
I think they claim ~2% increase??

Yes, but, there's a "but" the bmw is already prepared for that technology, has a massive battery in the trunk that costs a little fortune(about 260 us dollar).
People on drag races used to turn of the hidraulic steering assists and alternator, and it makes difference, but they remove it phisically(they remove weight).