Battery-powered electric trucks don’t carry an unlimited supply of energy. When the battery runs out, the truck stops. That’s why engineers do everything they can to squeeze every possible kilometer out of every kilowatt of battery capacity.

John Moore, the electric vehicle product manager for Volvo Trucks North America: With electric trucks, as you realize, there’s not a supply of energy that’s easily there all the time. It’s easily exhausted, it is not like diesel.

That’s John Moore, the electric vehicle product manager for Volvo Trucks North America.

Moore: One of the advantages of electric trucks is we can recoup some of the braking energy and put it back in the batteries instead of losing it all as heat through the brakes. With regeneration, all we’re doing is we’re reversing the polarity on the electric motors and turning the electric motors into electric generators. And at that point, the energy flows back into the batteries.

Capturing the kinetic energy of the motion of the truck is a very effective way of extending the range of the truck. In one real life extreme example, using regen braking on the long downhill grade between Flagstaff and Phoenix, Arizona, the truck could recoup enough energy—about 150 kilowatt hours, actually—to fully charge two Tesla Model 3 electric cars.

Here’s Christian Appel, the global head of product and programs at Nikola Motors, to explain.

Appel: Essentially, having the vehicle be controlled at a stable descent speed, you’re constantly braking, so to say, the vehicle—what you would normally do with an engine brake—and harvesting that energy. And, you know, given that differential in altitude and length of the route, there’s a significant amount of energy that can be recouped.

The amount of recoverable energy varies with the application, the weight of the truck, and the terrain. Like any other truck, the heavier it is, the faster it’s going, the more brake force is required to stop it. Thus, the more energy that can be recovered.

There’s not a great benefit to regen braking with on-highway driving because the brakes are seldom used. The real benefit comes with stop-and-go city driving. With some deft pedal control, experienced drivers of electric trucks can rely almost entirely on regen braking to slow and stop the truck.

Here once again, Volvo’s John Moore: If you drive it correctly, you can literally drive the trucks without even using the service brakes in the city if you allow yourself enough time and distance between other vehicles.

The driver has a great deal of control over how much regen braking force is used. Like the engine brake controls in a typical diesel truck, the driver can select between minimum and maximum recharging capability with several interim stops.

Nikola’s Christian Appel explains: The reason we do this is because it’s fairly convenient, like in a passenger car, to control your motion with only one pedal. But then in the truck, what the difference is—let’s say you’re going down a hill, and for a stretch of the hill, it’s between three and three and a half percent grade downhill for, let’s say, five minutes—you don’t want to be constantly on the pedal controlling the level of torque to stay at your descent speed. Right? You actually use now the six levels to put it in the right level. Let’s say in this example, it’s level four out of six. And you put it in level four to just keep the truck stable. Now you lift up your foot from both pedals and you just focus on your steering. So the idea is to use your lever to adjust to the right level of torque applied so you can stay at the speed you want without actually having constant foot on the pedal. Right?

Most trucks also have an automatic mode where the truck will optimize the regen braking to best suit the conditions and the terrain.

Regen braking works the same way with fuel cell electric trucks. They have batteries too, but smaller ones, usually about a third or less of the capacity of a full battery electric truck. Since the supply of hydrogen onboard is finite, any opportunity to recharge the battery through regen braking ultimately reduces the consumption of hydrogen.

Regen braking can also be managed with geofencing and predictive cruise control. If the truck knows its location, it can map out optimum charging opportunities along the route.

Fleets embarking on the electric truck journey should expect to do some work upfront. Drivers will need training on how to drive more efficiently, and there may also be a need to reexamine delivery routes to gain additional efficiencies through opportunity charging and diminishing load weights.

Just like learning progressive shifting back in the 1980s and adjusting to downsped drivelines in the early 2000s, regen braking is a concept that will take a bit of time to perfect. It will conserve energy and extend range for electric trucks, and it could also extend brake life and lower maintenance costs. And all that comes, basically, for free.