From talking to semi knowledgeable people in the auto-industrial lot over here, they say that the alternaotr is already fairly low drag when not under load.
Assuming that the cars own electricity management module cuts the load on the alternator:
What i could do is, have a minimum sized capacitor bank that is charged from an aux batter. Whenever i detect brakes being applied over canbus on the car (or throttle at 0 and not neutral gear or not clutch pressed and still moving) stop charging the capacitor so the alternator takes over charging it. Or stop charging it and divert power over to the aux battery.
Cars i will be working on will probably be post 2010
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