From all I've gathered about the HSD "B" mode is that it puts less juice back in to battery, using engine compression to slow u down on very steep downhills instead of the electric motors.

Said another way...as u go downhill the battery fills pretty good, up to the 'max' (on-screen it shows all green bars, in reality it's around 80%). So then the friction brakes are used, since the electric motors have no where to put the excess juice, thusly they are not slowing u anymore. So this is where u flick the gear selector into "B" mode and the engine is used to slow things down, instead of the friction brakes. Yet another way this car helps prolong a part (brake shoes)!

It controls the battery charge very tighly, it has a way to lessen brake shoe wear, it saves the air we breathe, it saves a depleting energy source...it's all good.

Love my Prius!

Curt.

'04 Seaside Pearl #7. Fumoto oil drain, mudflaps, rear bumper scuff protector & rear warn system, compass mirror, EV mode button, 8" subwoofer in right rear cubby & 6" subs under seats, power lumbar in the front seats, Coastaletech hitch w/ Aspen bike/snowboard rack. iPod2car, 2 amps, Alpine component speakers, and DVD video, solid 47 MPG @ 70000 miles.