On the road to electrifying vehicles, cars and small trucks are getting there. Big rigs, however, pose bigger hurdles.

The trouble with electrifying tractor-trailer trucks is that the tractor component needs more power than the current charging infrastructure can handle and the necessary charging time is long.

Major truck manufacturers like Volvo, Freightliner and Tesla are introducing electric tractor-trailer trucks, but that is still a tiny and inefficient market. Big rigs make up just 10% of the vehicles on the road, but they account for nearly 30% of total vehicle carbon emissions.

Now one startup, California-based Range Energy, is focused not on the tractor but the trailer. They are introducing electrified trailers that power and propel themselves so the tractor has less to pull.

“Everything that is built into the tractor is really built to manage the load of the trailer properly, and what we’re saying is, ‘Well, why don’t we do that directly through our Range system by electrifying the trailer in a way that has never been done before?'” said Ali Javidan, CEO of Range Energy.

The Range Energy system incorporates batteries, a motor that powers one of the trailer’s dual axles and what Javidan refers to as a ‘smart kingpin’ to improve the truck’s efficiency.

“When I push this button to activate the system, the trailer follows me,” Javidan said as he demonstrated the system. “It doesn’t matter if I’m an old Peterbilt semi-truck or a brand new Tesla semi or just me pulling on it with the system activated. The trailer’s mission is to make itself feel weightless.”

The electrified trailer can also refrigerate itself as well as power onboard communications and security systems. It does all of that at a fraction of the cost of diesel. 

“If we were to take one of these fleets that runs 3,000 trailers and run it through the range system and essentially incorporate the range system into their fleet, we’re looking at 100 million pounds of CO2 saved per year,” Javidan said. “But even better than that, it equates to about $50 million in fuel savings alone.”

Northern Refrigerated Transportation is piloting the Range trailers in California. The company has previously tried electric tractors but the long charging times were a hurdle, said Ricky Souza, COO at Northern Refrigerated Transportation.

Range Energy’s “trailers seem more of a natural fit because we have to load them, and we load them at night” while the trailers charge, Souza said. “So it’s not more dependent on a driver waiting for it.”

There are, however, some major roadblocks that Northern Refrigerated Transportation must overcome before the company can electrify its entire fleet of more than 300 trucks.

“There’s definitely some infrastructure challenges, like power to the buildings or properties and getting it, and the cost of the unit is more,” Souza said. “That’s part of doing the due diligence to see if you’ll make it back into fuel savings.”

Range Energy has raised $31.5 million so far, and it is backed by R7, UP.Partners, Trousdale Ventures and Yamaha Motor Ventures.

The appeal of Range Energy’s technology is the startup’s different approach to tackling the challenge of electrifying tractor-trailers, said Tyler Engh, R7’s founder and general manager.

“Seventy percent of all freight in the United States is done by trucks, and there’s no one touching a trailer, so if we can electrify the trailer, we could accelerate mass adoption for hybridization or electrification on current fleets that have diesel semis,” Engh said. “The size of what this company could become is exactly what venture capital is set up to do. It could be a humongous return for us.”

As in the EV market for cars, charging infrastructure is still not where it needs to be, but Javidan says trucking companies can leverage the power that’s available at loading docks, as Northern Refrigerated Transportation is doing. Javidan added that Range Energy is able to size the battery pack much closer to what you see in a passenger vehicle than what you see in the large commercial vehicles that are coming out from other big rig companies.

CNBC producer Lisa Rizzolo contributed to this piece.