BMW simply uses a slightly larger battery than is normal and only charges the battery via the alternator when the friction brakes are being used unless the battery charge starts getting too low.

 

If that is how it is being done, then I guess I wouldn't call it regenerative braking. To me, the word regenerative implies generating electricity rather than heat....

The way you described it, heat will be generated from friction brakes, and the alternator will still generate electricity, perhaps only being used while braking.


From Wikipedia: "A regenerative brake is a mechanism that reduces vehicle speed by converting some of its kinetic energy into a storeable form of energy instead of dissipating it as heat as with a conventional brake...."

 

I like the whine. I've heard it from outside the car (while someone else is driving), and it sounds like something straight out of a 'futuristic' sci-fi show from the 80s, where all the cars are supposed to be electric.