The Audi E-tron is one of a handful electric cars currently rated for towing. Audi recently showed off that capability with a very special payload.

An E-tron towed a trailer containing a General Motors EV1—the first modern electric car—from Tulsa Tech in Tulsa, Oklahoma, to the Fully Charged Live electric-car event at Circuit of the Americas, just outside Austin, Texas.

The total trip distance was 504 miles, according to Audi, and it wasn't made under ideal conditions.

The trailer and payload weighed a combined 4,000 pounds, according to Audi, which also happens to be the E-tron's maximum tow rating. The trip was also made in 35-degree weather, with rain throughout, according to Audi.

The E-tron was charged at Electrify America DC fast-charging stations along the route. Capable of charging an E-tron at up to 150 kilowatts, these stations are built using funds from Audi parent Volkswagen as part of its diesel emissions settlement.

Audi did not say how many charging stops were made, but that average efficiency with the trailer was 1.3 miles per kilowatt hour at an average speed of 60 mph.

2019 Audi E-Tron - Best Car To Buy 2020

2019 Audi E-Tron - Best Car To Buy 2020

The E-tron has a 95-kWh battery pack, but only 88% (83.6 kWh) is used. That means the SUV was averaging 108.6 miles per charge (or likely quite a bit less, practically) while towing. The E-tron has an EPA-rated range of 204 miles per charge when unladen.

Towing a trailer requires a lot of extra energy, and most electric cars simply don't have that extra energy storage capacity in their battery packs to still present respectable range. This isn't a problem for internal-combustion vehicles, because gasoline and diesel are so energy dense that it doesn't matter if they use twice as much energy while towing.

As Audi demonstrated, the availability of DC fast-charging stations can compensate for that, as long as the driver is willing to make more charging stops.

Similarly, drivers of the Tesla Model X—the only other electric car currently on sale that can tow—can rely on the Silicon Valley automaker's Supercharger network.

Tesla Model X towing

Tesla Model X towing

The Model X is rated to tow 5,000 pounds. That's 1,000 pounds more than the E-tron, and about the same as most gasoline midsize family SUVs.

The upcoming Polestar 2 has a 3,300-pound tow rating.

All of these vehicles will likely be eclipsed by a gaggle of electric pickup trucks, from Ford, General Motors, and Tesla, as well as newcomers like Rivian and Bollinger.

Some of those automakers are already making bold claims about towing, but owners will have to consider the effect towing a heavy trailer will have on range.