5 Reasons Public DC Charging Is Slower Than Expected

If you check out the specifications of a public electric vehicle DC “Fast Charger” you will see a rating listed in the unit kW (kilowatt). This power rating is intended to inform those who charge in public how quickly the vehicle can be charged. Or maybe we should say it indicates a possible power rating that the equipment could theoretically supply. The truth is many public DC fast chargers display a power rating they have never once delivered to a single car.

Related Story: Testing the Fastest Car at the Fastest Charger

Electric car and EV charger companies have a vested interest in convincing EV shoppers and owners that cars can be charged quickly on the go. After all, at their core, cars are about mobility and convenience. However, the methods adopted to communicate how electric vehicles charge are murky, often inaccurate, and one might argue purposefully misleading. Those could be opinions. Rather than offer our opinions on how DC charging works and why it is slow, we’ll let the folks who make the chargers and the cars explain how public DC charging works and let them offer reasons or excuses why the numbers they offer are not the numbers that folks charging cars actually see.

1) The Imaginary 350 kW Charging Rate
The most cut-and-dried example of an unfulfilled promise around public DC charging is the 350 kW-rated charging station. We communicated with an employee of a major DC charging company in America. He told us, “There is no vehicle on the market that can accept 350 kW. The Porsche Taycan has the highest speed at 270 kW. However, even the 238 kW (Hyundai Ioniq 5) is ideal when the battery is pre-conditioned, and the ambient temperature is ideal.”

So, just to summarize, although public DC “fast chargers” are adorned with the number 350kW, and you will see that number on apps that help to locate DC fast chargers, no cars can come close to using that power - if it were even actually available. Which it often is not, as number two explains.

2) If Others Are Charging, Your Rate Is Dramatically Lower
Many DC chargers display a very high power rating (for example, 350kW), but that power is lower if another vehicle is charging nearby. Charging spots often share their power delivery source with one another. This is called active power sharing, distributed load, or distributed power. So, let’s say one pulls into an open “350 kW” charging spot while another car is already charging in the adjoining spot. Sure, your car can’t accept that power, but it can take a lot. So, what might the true power be? The charger company employee told us, “With active power sharing, 150 kW...” Why 150 and not 350 kW? Because the total available power is being split between two charging spots. Dividing by two does not help here. Half of 350 kW is 175 kW, yet just 150 kW may be the most the charger can offer.

3) Battery Charging Curves
Although many, if not all, 2024 and 2025 model-year battery electric vehicles advertise their charging performance on 350 kW chargers, they can’t accept anywhere near that amount of power, as the charging company employee explained. But many can accept well over 200 kW. That’s a lot of power, and it would be great if it was as simple as one number. However, batteries in today’s electric vehicles don't always accept power at their maximum rate. Rather, that maximum is only available in a very short window of their overall battery capacity.

Battery capacity is often referred to as state of charge (SOC). It’s the 0-100% number we all recognize as how much charge the battery is holding. When a battery is discharged to a point near being “empty,” it can accept power at near its maximum rate. However, as it charges up, its ability to accept power drops off dramatically. A battery pack and onboard charger that is rated at “238 kW,” for example, may only be able to draw well below 100 kW, even at its 50% state of charge point. After around 80% SOC, the battery’s ability to accept power drops dramatically down, pointing toward zero. Our contact at the charging company told us, “If you research charge curves for this vehicle, you can see that the vehicle starts taking less power after 50%.” This was in the context of a vehicle charging at a station displaying 350 kW and a car that advertises its charging capability using 350 kW chargers. What did we observe? Rates as low as 84 kW.

You may have noticed that the charging company employee told us to "research the charging curve." If only it were so simple. We've never seen an EV charging curve in any owner's manual or any specification page available to the public. Furthermore, we've never seen one printed in any press releases by any EV manufacturer or seen a charging curve offered as part of any specification page on the media pages for EV manufacturers. This isn't data that is available to consumers from the automakers that make EVs. If this information is important to understanding how a car will charge, it should be easily found and openly supplied by the automaker itself. Bloggers and EV advocates end up creating these curves, but as we will explain below, the curve is not the same from one day to the next. 

4) Environmental Factors Reduce Charging Speeds
Thus far, we’ve been discussing DC charging as if the car and the charger were the only variables. They are not. As our charging company contact told us, “Actual charging time varies based on a number of factors, including current battery charge level, output of the charging unit, vehicle and battery settings, battery temperature, and outside temperature.”

Cold is the real enemy here. Cold batteries and cold chargers result in reduced charging speeds. Vehicles can help to deal with this by conditioning their batteries in advance of charging. It does not solve the problem, but it can help.

Heat can also be a factor that reduces charging speeds. If you followed the news about EV charging, you likely saw the stories about EV owners using wet cloths draped over charging handles when DC charging in an effort to help cool the equipment and deliver a faster charge. Don't be that guy. We only offer the point to show that environmental factors can and do reduce charging speeds in the real world. 

This past January following some bad press, Ford issued a handy list of best practices to its customers related to winter charging titled, “Winter Is Here: Tips for EV Drivers in Extreme Weather.” In its guide, Ford says, “Precondition your vehicle before use to warm the battery while plugged-in: By preconditioning your vehicle, you’re allowing the battery to warm to optimum temperature before use, positively affecting range and driving dynamics. For Ford EV owners, preconditioning can be scheduled using the vehicle’s SYNC touchscreen or from the comfort of your couch using the FordPass app.  Use your vehicle’s Ford Onboard Navigation to locate a DC Fast Charging station - In doing this, the vehicle preconditions by warming up the battery within 20 miles of your destination. This allows the battery to accept a charge faster in cold weather, getting you back on the road quicker.” As you can see, charging requires some forethought and planning, and automakers are offering user guides and apps to help EV owners manage the long list of things they need to consider related to charging.

5) Utility Constraints
When we reported on Ford’s massive investment in public charging, one thing we uncovered was that the projects took a very long time to complete and that the chargers were not as highly rated in some areas as in others. Off the record, we were told by a dealer that the power available to its location was one reason its chargers were not higher in power and that the chargers would have been online many months sooner if the utility company had the resources to make the final connection.  Without any corroboration, we did not highlight those statements in our reporting. 

However, in our conversations this week with a charger company, it came up again. We were told, “Due to utility constraints, Balance chargers are a way to be able to add more chargers and distribute power based on energy demands.” These two sources have reported that they could have offered more power and higher charging speeds, but the local power utility company would not provide it. 

The steep rate of electric vehicle adoption slowed over the past two years. Early adopters have all purchased an EV, and a lot of early adopters have had many EVs. The full-court press by governments and EV advocates has not resulted in the hoped for rapid market share gains. Why?

A Harvard Business School study published this summer concluded that a major barrier to EV adoption is "A deep frustration with the state of charging infrastructure, including unreliability, erratic pricing, and lack of charging locations."

A Science Direct Study found that "Longer charging times are the most frequently cited barriers to consumer's EV adoption."

A Transportation and Environment study says that "Charging time compared to refilling with petrol was a top concern for 9% of people and was a concern for a further 23%."

One big reason EV adoption has not continued its steep pace is that EV charging remains confusing and frustrating, even to experts. Those who have not opted to purchase a battery-electric vehicle have their reasons. Untrustworthy public charging speed is obviously one reason why shoppers have second thoughts. 

Author note: Torque News offered to name the charging company employee who provided the quoted input, but he preferred to remain anonymous. 

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John Goreham is an experienced New England Motor Press Association member and expert vehicle tester. John completed an engineering program with a focus on electric vehicles, followed by two decades of work in high-tech, biopharma, and the automotive supply chain before becoming a news contributor. In addition to his eleven years of work at Torque News, John has published thousands of articles and reviews at American news outlets. He is known for offering unfiltered opinions on vehicle topics. You can connect with John on Linkedin and follow his work at our X channel. Please note that stories carrying John's by-line are never AI-generated, but he does employ Grammarly grammar and punctuation software when proofreading. 

Top of page image by JOhn Goreham.