For electric vehicle (EV) drivers traveling through Wyoming, the Smith's grocery store in Rock Springs serves as a convenient stop. Located just off I-80, it's close to a Petco and features six chargers, each advertised to provide 350 kilowatts of power. At that rate, a Tesla Model 3 could be fully charged in the time it takes to make a quick stop for the restroom and a snack.
However, when the author arrived at the station last month, driving a Rivian R1S with one dog and two kids, the promise of 350 kW seemed out of reach. The Rivian SUV, which has a maximum charging capacity of 220 kW, was further limited by the station, delivering only 50 kW. As a result, the seven-hour road trip became two hours longer due to the slower charging.
This issue is not unique to Wyoming or Rivian vehicles. According to Stable Auto, which assists in planning new charging infrastructure, the average charging speed at US public stations that promise 100 kW or more was only 52 kW in 2022. This discrepancy, primarily due to the complexities of battery power, leaves many drivers unsure about when and why their charging is being throttled. David Slutzky, chairman and founder of Fermata Energy, a company developing vehicle-to-grid charging systems, explained that fast-charging infrastructure is not fully developed, and most stations reduce the charging speed quickly.
There are several reasons why even the most advanced public chargers rarely deliver maximum power. Unlike filling a gas tank, battery charging involves intricate chemical processes, with both internal and external factors affecting speed. For example, not all EVs can charge at high speeds. Of the 55 electric models available in the US, half can charge above 200 kW, while only five reach 350 kW. Additionally, extreme temperatures, whether hot or cold, can slow charging to protect the battery. As the battery approaches full capacity, charging naturally slows down to prevent overheating, a process similar to how smartphones and laptops charge. Each vehicle has its own unique charging curve, though automakers are often reluctant to disclose these details. For instance, Tesla vehicles have steeper charging curves, which means the "fast" charging phase is relatively short.
