Regenerative braking is a system that’s used by electric (and hybrid) cars to recover some of the energy that’s normally lost when a car slows down. 

The electric motor works as a generator, converting some of the car's kinetic energy into electricity and sending it back to the battery.

But how does it actually work, does it increase your range, and what's the difference between regenerative braking and normal brakes? Here's everything you need to know.

What is regenerative braking?

When you hit the brakes in a standard petrol or diesel car you lose all that forward energy as heat and friction, but one of the neat tricks that an electric or hybrid car has up its sleeve is brake regen (as it’s also known). 

This stores up energy in the battery that would otherwise be wasted under braking. It’s all automatic (some cars let you adjust how strong it is using paddles, steering wheel buttons or the touchscreen menu) so you don’t have to worry about it. 

Is regenerative braking the same as normal braking? 

They’re the same in the sense that they both slow the car down, but regen uses the resistance of the electric motor to slow the car down and recover some energy, while conventional friction braking presses brake pads against a disc on the wheels to slow the car down. 

EVs have both systems on board, but use the regen to maximise efficiency and the conventional brakes when they’re needed. If you were to do an emergency stop, for instance, it would be the friction brakes doing most of the work. 

How does regenerative braking work?

Electric motors work when electricity passes through sets of wire coils that sit inside a ring of magnets. 

As the coils are energised they generate an electromagnetic field, different parts of the rotating mechanism of the motor are attracted and repelled by the outer magnets and it spins round. 

So if you put in electricity, movement comes out, but if you reverse the process and put in movement, electricity comes out. 

Regen uses the movement of the car to turn the motor, generating electricity and providing a resistance that slows the car down. The amount of resistance allowed is controlled by the onboard computer, so it feels nice and steady. 

Does regenerative braking charge the battery?

It does charge the battery, this is the main benefit of regenerative braking, though cutting down on wear and tear on your brakes is a happy side effect. Not that we have to spend that much money on our brakes, but every little helps. 

Regen is what makes EVs so efficient around town and in traffic jams – with all the stop start traffic and braking going on you can really use it to your advantage and juice up the battery. 

Does regenerative braking increase electric car range?

Regen can increase the number of miles you get from a battery, but you won’t often see your remaining range actively go up on the dashboard unless you’re descending a gigantic hill. 

Regenerative braking is the main reason that your efficiency is so much higher around town than on the motorway – you’re recovering energy as you go that would otherwise be wasted. 

What does regenerative braking feel like?

When you come off the accelerator, regen just feels like good old-fashioned engine braking. You can feel the car slowing down, but in a very steady fashion. 

The only disconcerting part of the process – and it’s probably only driving geeks like us who would be bothered by such a thing – is the transition between regen and the friction brakes, which happens just before you come to a stop. 

Carmakers have got a lot better at managing that handover between regen and brakes, but you can still sometimes feel a jolt or roughness in the pedal. Or if you’re braking more forcefully there’s a bite as the friction brakes kick in. But it’s nothing to worry about. 

What is one-pedal driving?

One-pedal driving is a bit like being on the bumper cars (bear with me here), in that you just need the one pedal to go and stop. Come off the pedal and the car will slow down. 

Unlike the bumper cars, if you crash into someone in your EV it’s going to be a nightmare with the insurance, don’t do it. 

With proper one pedal driving the regen is generally set to its maximum and coming off the accelerator will bring the car to a full halt. It’s quite satisfying once you work out how much distance is needed and nail a stop at the lights. 

In cars like the Volkswagen ID.4 below, you can also get adaptive regen that changes the strength based on the corners coming up or how the traffic in front of you is behaving.

Can you turn regenerative braking off?

Sometimes you can and sometimes you can’t, it really depends on the carmaker. It can be useful to turn it off on the motorway so that when you come off the accelerator you’re just coasting – you can get a surprising distance on a slight downward slope. 

It’s best to turn the regen back on though, or at least use the brake pedal to slow the car down, otherwise you will crash into something. 

When does regenerative braking not work?

If you’ve just unplugged the car and it has charged to 100% you will find that the regen doesn’t work. It can be a surprise if you’re not expecting it. 

Because the regen charges up the battery, if the battery’s full then it has nothing to charge up and so the computer brain won’t let the car do any more charging, so if you come off the accelerator you’ll just find yourself coasting along. 

There might be other scenarios where the car will turn off regen – if the battery is too hot or too cold, for instance. But at least you still have your friction brakes to rely on at that point. 

When does regenerative braking turn on the brake lights?

This is an interesting one – the brake lights are legally required to come on once deceleration reaches or exceeds 1.3 metres per second squared, which is around 0.13g. 

But it’s at the carmaker’s discretion whether the brake lights come on below that – if you touch the brake pedal in a car it usually means the brake lights come on, but coming off the accelerator with regen set low won’t always turn the brake lights on, but with stronger regen it will. 

My personal preference in each EV I drive is to find the regen setting that’s as strong as it can be without turning the brake lights on all the time, but that’s just so they don’t flash in Morse code every time I twitch my right foot. 

And now we’ve reached this level of chat, it’s probably a good time to call it quits.