Public electric vehicle charging stations in America have a bad reputation. They’re notorious for breaking down, charging at a snail’s pace, refusing customer payment and leaving drivers stranded without juice.

Advocates for electric vehicles, or EVs, worry that reliability concerns are hampering adoption at a critical moment in the campaign to reduce greenhouse gas emissions, but data on the topic is limited.

To address this problem, researchers at the University of Washington designed a survey to tease out exactly how much a car owner’s perception of public charging reliability influences their willingness to buy their first EV. The research was published in Transport Policy.

The team created a series of hypothetical scenarios to study the factors that might nudge a skeptical shopper towards an EV over a gasoline-powered car, including vehicle and gas prices, driving range and public charging access.

The results were dramatic. Participants with a negative view of public charging were much less likely to choose an EV than those with a moderate view. It took some serious hypothetical improvements to offset those negative perceptions: The EV needed to be discounted 30%, have 366 extra miles of range or there needed to be 30,000 additional public charging stations.

“No one knew how much charger reliability was coloring the decisions of prospective EV buyers,” said senior author Don MacKenzie, a UW associate professor of civil and environmental engineering.

“I was not at all surprised by the direction of the response. What surprised me was the size. These were monster results. This is a warning for the whole industry.”

The results come at a tenuous time for EV adoption in America. The market continues to grow, but political factors like the end of federal tax incentives are complicating sales outlooks. The federal government is also challenging California’s plan to phase out gas car sales, which could threaten similar efforts in Washington and several other states.

The state of public charging isn’t inspiring confidence in buyers, either. Studies in recent years have shown significant reliability issues with public networks. There are signs that the situation is improving, and home charging is an option for some drivers, but the threat of slow and flaky public chargers remains a powerful deterrent for anyone venturing outside their “home range.”

“We know there’s a lot of range anxiety out there,” said lead author Rubina Singh, a UW doctoral student of civil and environmental engineering. “EV owners often tolerate charging problems, while newcomers are less aware of the hurdles. If trust erodes, adoption could slow.”

The team found it tricky to measure the link between station reliability and buyer behavior because there weren’t obvious real-world groups to compare. Tesla’s stations get consistently higher marks than other networks, but Tesla cars and their owners are too different in other ways to make for a useful comparison. Simply asking people for their thoughts about charging may produce answers that are colored by their overall feelings about EVs.

Instead, the researchers turned to hypothetical scenarios. They recruited roughly 1,500 participants who had never owned an EV and surveyed them in three groups, asking the first to picture a world where public charging is a mess, the second to imagine a charging utopia and the third to simply give their preexisting opinions about charging.

Each group then went “shopping.” Each round of the survey, participants chose between an EV and a comparable gas-powered car. The researchers tweaked variables such as vehicle cost, gas prices and range, and trends emerged over several rounds.

Participants with a negative view of public charging demanded strikingly large concessions before choosing an EV. In some cases, the adjustment needed was nonsensically large.

“People wanted a 366-mile increase in range before they bought an EV,” MacKenzie said. “Lots of EVs don’t even have a 366-mile range today. That’s obviously not a practical demand. But it illustrates the strength of this effect.”

There were other surprises in the data, too.

“The results were basically the same for people who have access to home charging and people who don’t,” Singh said. “So even if they wouldn’t actually have to rely on the charging network, respondents were still concerned about reliability.”

As the auto industry works to bring EVs into the mainstream, these findings are both a warning and an invitation for further study. Little is known, Singh said, about what specific improvements would have the greatest impact on public charging perception. Asking the right questions could help stakeholders throughout the industry figure out where to invest.

“What are the specific factors that would convince skeptics?” she said. “Does a station need to be online 90% of the time to improve a user’s perception? Or 95%? Or 99%? Or would improving the point of sale system help more? Where do you put your dollars to have the greatest effect on public perception?”

What’s clear, MacKenzie said, is that reliability must be prioritized as charging networks expand.

“This is the Achilles’ heel right now for EVs,” he said.

“If we push the broader market towards EVs, or if it grows on its own before we can fix this problem, it’s really bad news for continued growth. I think it could engender a real backlash. It only takes one bad experience to lose a customer. That’s a big danger for EV adoption.”