By Kyle Stock

For EV drivers in Wyoming, the Smith’s grocery store in Rock Springs is an oasis. It’s just off I-80, there’s a Petco across the street, and it has six plugs promising to charge at 350 kilowatts. At that rate, a Tesla could go from empty to full in the time it takes to hit the bathroom and grab a snack.

But when I limped up to the station in a Rivian R1S last month, that 350 kW may as well have been a mirage. Rivian’s SUV charges at 220 kW at best, and the charger itself crimped the hose to just 50 kW. With one pit stop, my carefully planned seven-hour road trip got two hours longer. At US public stations with charging speeds of 100 kW or higher, the average delivered charge was only 52 kW in 2022, according to Stable Auto. That disconnect — largely a reflection of battery power’s idiosyncrasies — is leaving US drivers guessing as to when, why and by how much a charge is being throttled.

“We really don’t have a fast-charging infrastructure today,” says David Slutzky, founder of Fermata Energy, which builds vehicle-to-grid charging systems. “They are almost all ratchet down the charge pretty quickly.” There are a variety of good reasons why even the slickest public chargers rarely run at maximum capacity. The chemical wizardry of battery power is more complex than pouring liquid in a tank, and both internal and external factors take a toll on charging speed.

For starters, an EV itself can only suck up electrons so quickly. Of the 55 models now available in the US, half charge above 200 kW and only five can charge at 350 kW. Those speeds are further compromised when it’s very hot or very cold; automakers program their cars to slow a charge during temperature extremes to avoid damaging the battery.

Trickier still, EV charging slows naturally as the car’s battery approaches full, to keep it from overheating. (Smartphones and laptops do the same thing.) The specifics of this charging curve are unique to each car, though brands are cagey about sharing those specifics, even with buyers.

Finally, charging networks themselves crimp electron flow. On a hot day, the local grid might be maxed out, or the plugs’ hoses may be close to overheating. Many stations split power between cars, allowing them to install more cords with the same electricity. In other words, a 200-kW charger becomes a 100 kW charger when someone uses its second cord.

“There’s sort of this complicated handshake between the vehicle and the charger, so I think there’s an education gap for sure,” says Sara Rafalson, executive director of policy at EVgo.

That gap risks hurting EV adoption in the US, where charging speed has become a marketing metric. Automakers trumpet how quickly their cars can go from 10% to 80% full, while public charging stations display maximum charge rate — not average or expected — right on the machines. Some 17% of US public chargers are rated 100 kW-plus, according to BloombergNEF, compared with 10% in the UK and 2% in the Netherlands.

“We still see a lot of discrepancy between what the customer is expecting and what they’re seeing at the site,” says Anthony Lambkin, vice president of operations at Electrify America. “The great news is we have a lot of new drivers, and this is just one of those learning-curve things.”

Consumers are slightly less sanguine. In a recent JD Power survey, EV owners scored public charging speeds near the bottom of 10 categories studied. Brent Gruber, executive director of JD Power’s EV practice, says people develop false expectations “when you plaster those [kilowatt] numbers on the charger itself.”

While charging’s inherent complexity means the speed gap will never close entirely, it should narrow over time. Charging networks are building faster and larger stations in the US, which will ease the need for power dilution across plugs. And carmakers have realized that max charging rate is a deciding factor for car buyers and are dialing it up on coming models.

But for the time being, the best way to cope with the unpredictability is to prepare for it — something I was paying for not doing in Wyoming. After about 15 minutes of 50 kW charging in Rock Springs, I cut my losses and drove 100 miles north to Pinedale, where two cords idled in a dusty lot behind Stockman’s Saloon and Steakhouse.

With a maximum charging speed of 120 kW, the Pinedale plug should have been far slower than the 350-kW machine in Rock Springs. But I only had 90 miles to go and it covered that in just a few minutes.