I have noticed lately that my prius shows the all black (no arrows) energy screen with my foot not on the accelerator or the brake pedal. This always happens right around 7mph. Has anyone else experienced this? I am wondering if it has anything to do with the switch to friction braking. The first time I noticed was about a week ago but now I see it pretty consistently when coasting at 7mph.
Yeah, there's definitely a point - around 7MPH - at which regen is inactive and no battery power is used. It's been my observations that below ~7MPH the battery will kick in to maintain momentum. At speeds above ~7MPH the regen will activate. I have a four-way stop on my regular commute that I often have to creep about a quarter-mile to at speeds below 10 MPH.
There's actually a tiny battery drain at those speed (a few amps), but it's below the ~7 amp threshold needed for the display to show it.
