Between 33% and 50%. This is better than throwing it all away like friction brakes do, and because the motor/generators (MG) have already been paid for it's essentially free. But it's better to glide to a stop when when possible because then the energy is turned into motion rather than having part of it turned into heat.
The most efficient regenerative braking is achieved when the brakes are lightly touched--just enough so that you can tell the brakes are working.
Gliding means that the accelerator pedal is pressed just enough so that (at speeds 41 mph or less) there are no arrows going anywhere on the Energy screen. Over 41 mph needs the same amount of foot pressure but yellow arrows will show because the engine spins to control the speed of the smaller MG.
Wayne B., a Yahoo Prius group member, put some instrumentation on his Prius and measured these numbers. Note that these numbers just compare various types of braking, not braking compared to gliding.
WB> Here is a table that illustrates the several common ways we slow the
WB> Prius down and their ratings in efficiency percentages. "Braking @
WB> 60 Amps" is the most efficient way to slow the 2004 Prius down;
WB> therefore it is the 100% baseline or benchmark against which the
WB> others are compared:
WB>
WB> Mode.....................Efficiency
WB> Braking @ 60 Amps...........100%
WB> Braking @ 70 Amps............91%
WB> Drive..(coasting)....................84%
WB> Braking @ 90 Amps............76%
WB> B mode.(engine braking).......68%
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Linear Mode
