It's simply the momentum of the car pushing electrons back into the battery when you let off on the spark pedal.
The Bolt has a little regen hand paddle that can be used in lieu of brakes when you want to slow, the brakes are also 100% regen (no pad contact) for the first bit.
Just for fun go...
Bolt driver, day two reservation.
Just checking if the Slate has a steering wheel regen paddle like my Bolt or is it just on/off electron pedal?
Looking forward to the 24th, just added a roof rack to my base Slate as the only option.
Search indicates not.