Could Regeneration overcharge the battery?

That's my understanding. So if the battery is full (even including that portion which is beyond access to the end user) then ...... ? No regen braking and we rely on friction brakes alone? I get that I am positing an extreme scenario and it does not keep me up at night in the least. I am just trying to get a better picture of how the magic works behind the curtains.

 

well, assuming your memory is correct, it's two possibilities:

1 - the dash warning is misleading, it's telling you that you shouldn't try to regen but it is still doing some regen. perhaps not the max it can, but still slowing down the car. when the battery percentage shows 100% the battery is not really full, some regen is still available based on my own test.
regardless of the dash message, you can always look at the power meter: if the dash says regen not available but you see blue lines in the power meter, power is going to the battery.

2 - no regen is possible so when you hold the paddle, the car actually applies the mechanical brakes. it has the capability in the braking controller, so it could be doing this.

 

Oh yes, good point. I would say that applied more to manual cars than automatic (though even auto vehicles have L gears that can help, as long as you don`t over-rev). I suppose if you are driving up the mountain, you will still have plenty of space available for regen to get you back down safely. If you are charging on the top of the hill, it would be good to leave some space empty for that free energy à la "hilltop mode".

I seriously hope I never have to use an electronic e-brake either.. Really gonna miss my manual e-brake; activating it momentarily has saved me the odd time my car has completely lost traction around a corner in the winter (going like half the speed of suggested speed limits with winter tires!)