The only point at which an EV with regen will coast is when the speed set by the r/h pedal is equal to the road speed - normally when the potential acceleration through running downhill is balanced by wind resistance and friction forces.

Too steep a hill and the brakes will regen to reduce speed to that desired/set. Whether the brake lights illuminate depends on sensitivity.

My normal petrol auto in cruise control sometimes does much the same thing going downhill - but as there is no regen, it will slip down a gear or two to get some engine braking.

In a normal manual we normally accept that on a downhill slope speed may increase slightly - it usually scrubs off as the road levels out.

With the gentle gradient witnessed today I think wind and rolling resistance would be enough without braking being required. I can't see why brake lights would be programmed to come on unless the car is actually slowing. If I lift off the gas and my car slows, the lights don't come on and I wouldn't expect an EV's to either. I'd have assumed the rate of deceleration would have to exceed a predetermined point to trigger. From what's been previously said, an EV can (should?) be driven on the accelerator, so no coasting in regen mode.

Downhill in an IC car, the brakes can be used to prevent the speed increasing - so brake lights and deceleration don't always co-incide.

With the gentle gradient witnessed today I think wind and rolling resistance would be enough without braking being required. I can't see why brake lights would be programmed to come on unless the car is actually slowing. If I lift off the gas and my car slows, the lights don't come on and I wouldn't expect an EV's to either.

Nor would I, it would put out conflicting messages to a following driver, making them hover over the brake pedal more often than they need to. The brake lights should only come on if the driver is actually braking in my opinion.

The flickering brake lights isn't limited to drivers in EVs.

Most of the time, it's caused by people who drive automatics with both feet.

The flickering brake lights isn't limited to drivers in EVs.

Most of the time, it's caused by people who drive automatics with both feet.

That's very much a minority among drivers of automatics - most ignore the questionable advice to "left-foot brake"

Left foot braking when driving an automatic is advised at maneuvering / parking speeds only.

It's not questionable, it's sensible.

A third point about "phantom braking" is regarding the ever more common cars equipped with "Auto Hold", whereby the car's brakes are applied and held on automatically whenever the car comes to a complete standstill, e.g. at traffic lights, and it is in neutral (manual or, IIRC, automatic alike).
In a recently hired Golf I found that in neutral, at standstill, once I released both clutch and brake pedal, the Auto Hold circuit kicked in and the car continued to apply standard foot braking - meaning that the brake lights remain on. I also found that if I then flipped the separate parking brake switch, the Auto Hold disengaged and standard "hand" brake was applied. WIth either type of automatic braking, there was enough braking force to carry out smooth hill starts.
The downside to this generally clever and useful system - which can of course be switched off - is that if a driver on "Auto Hold" decides not to engage the parking brake, the brake lights remain lit and can dazzle the driver(s) behind for however long the traffic queue/traffic lights hold the drivers up.

Also heavy goods vehicles will have the brake lights on a lot going downhill, for obvious reasons, although a lot of them can use engine braking and / or secondary braking, such as a retarder. This poses another question which I'm about to Google for an answer. Do the retraders on HGVs trigger the brake lights if they are full on?

Not a quick answer, depends on the make, the 2 Swedish makes do, some German ones don't, can't recall what Dafs do.

Personally i don't like the brake lights being triggered for something like the typical exhaust brake, at best on long motorway descents they will hold speed steady yet the brake lights on those that do trigger the lights can be on for more than a mile continually, unecessary when the speed hasn't altered.

This answer re the brake lights applies when only the standard exhaust or engine brake is fitted, real retarders and brake lights could be different but are so seldom specified for UK market (accountants and typical supermarket transport managers probably don't know what one is) and so few hgv licence holders know how to retard a loaded commercial vehicle properly that it would be pointless to spec them anyway...hgv drivers are taught 'brakes to slow gears to go' these days, you almost never see an HGV driver going down through the gears maximising auxilliary braking or holding speed steady via such things.