The news was inescapable. Against the backdrop of record-low temperatures, Tesla drivers in the Chicago area were literally abandoning their cars at Supercharger (Tesla’s name for its proprietary charging network) locations and, ironically, catching rides home in gasoline-powered vehicles.
Tesla Charging Apocalypse: What Really Happened in Chicago
First reported by Chicago’s Fox 32 TV News a couple of days ago, the dead cars, lines to charge, and the reported frustration of drivers, seemed to vindicate what electric-vehicle naysayers have been claiming for years now: EVs aren’t ready for primetime. The story has been shared by Fox affiliates nationally, and has been quoted in literally hundred of articles and blog posts.
Indeed, the situation depicted was grim, but there is much about the situation that was not—and largely still has not—been reported about the incidents in question. Let’s try and straighten a few things out:
Given
It was very cold
This past Sunday, the high temperature in Chicago was 1 degree. Area suburbs did not see temps over zero. It was really cold.
Cars were not being charged
Drivers reported that though they were plugged into Superchargers, and connected properly, charging did not take place. This is true-ish, but there’s more to the story. Keep reading…
Drivers were abandoning their cars
Based on the images provided by Fox 32, it seems clear that a number of Tesla owners gave up on their cars and found alternative transportation. At this point, we’re not suggestion that the Fox 32 report was factually in error, only that there is so much more to the story.
More to the Story
The Superchargers were not (entirely) the problem
It is important to realize that Tesla Supercharger stations are located in Northern Minnesota, remote parts of Canada, and in Sweden. These locations often see temperatures as low as those that recently frosted Chicago, and by all accounts, the Superchargers in those locations work as expected and their operation is not significantly compromised by the cold.
Lots and lots of new Tesla drivers
Tesla sales have increased dramatically over the last few years—now exceeding two-million units a year globally—and many of those recently acquired Tesla cars are owned not by old-school brand fans and loyalists, but by mainstream consumers, most of whom are not as EV savvy as the early adopters. We’ll get into why this matters in a moment.
Fortunately, where the news fails, and where hard facts are scarce, there are message boards, and that is where this story begins to flesh out. And it’s a compelling tale…
What Really Happened
As most consumers are likely aware, EV batteries are a little finicky about the temperature. In fact, EV batteries, especially lithium-ion batteries (Li-ion) like the thermostat about where humans like it, with temperatures above freezing, and below 90 degrees. In Consumer Guide testing, we find that EV batteries perform best—by returning the greatest driving range—when temperatures hover in the 50-to-60-degree range. Such mild temps are often accompanied by real-world driving ranges in excess of official EPA estimates.
Cold especially saps EV battery potential, by as much as a third when the thermometer drops to around freezing. But it isn’t just a battery’s ability to provide power that is compromised by cold, it is also its ability to be charged, and this is where things get interesting.
To facilitate faster and more efficient charging, many electric vehicles provide for something called “preconditioning,” a process which incorporates a thermal-management system to raise a battery’s temperature prior to charging for optimal charging speed and efficiency. Preconditioning can significantly reduce charging times.
(Note that even without preconditioning, an EV’s thermal management system will, in most cases, raise the temperature of a cold battery while it is being charged, but this process takes time, lengthening the duration of a charging session.)
Now, all current-model Tesla vehicles feature a preconditioning system. And—this is interesting—the system is automatically engaged when Tesla owners use their onboard navigation system to connect with a Supercharger. This means that, on the drive to the Supercharger, the battery is automatically being warmed.
(Note: Using the navigation system—or charging app—allows Tesla drivers to locate and reserve an operational Supercharger unit. Once reserved, the car’s thermal management system can begin readying the battery for charging. This system is not unique to Tesla cars, though not all EV vehicles employ a similar preconditioning system.)
Unfortunately, preconditioning requires energy, and the energy is supplied by the EV battery. Some estimates put the amount of energy required to fully precondition a battery on a cold day at as much as five percent of total battery capacity.
Bad news…
In a nutshell, we have cars suddenly losing battery capacity due to the cold snap, preconditioning further sapping batteries, and cars charging slowly—possibly very slowly—and you have the backdrop for a horrible experience at a few Supercharger locations. Note that we said “a few,” we’ll get back to that point in a moment.
So slow, it seemed as if nothing was happening…
Based on plenty of research, here is what we think happened. As the temps dropped, a large number of Tesla drivers found their batteries rather suddenly at a low state of charge. Many drove to the nearest Supercharger location, and we’re guessing, did NOT precondition their batteries along the way.
(Preconditioning note: It is possible to initiate the precondition process manually from inside the car. However, the process will not commence if the battery is below a certain level of charge. We suspect that a significant percentage of the Teslas involved in the chaos reported by Fox 32 were not preconditioned upon arrival at charging stations.)
The problem:
The batteries of non-preconditioned Teslas were so cold that charging was not initially possible. Much evidence suggests that time initially spent hooked-up to the charger was spent delivering energy to warm the battery—time during which it appeared to drivers that no charging was taking place, which is technically correct.
We don’t know how much time was needed to bring batteries up to operational temperatures, but suspect many owners abandoned the process—and their cars—in frustration. While some drivers gave up on the charging process, others reported extremely slow charge rates, as low as 25kW (many Superchargers deliver charging at as high as 180 kW) The long charge times would have contributed to the lines reported at Supercharger stations.
Some complicating factors
New Owners
As a pioneering EV manufacturer, the Tesla ownership base has long been comprised of brand fans and loyalists, many of whom are very well acquainted with the workings of their vehicles. A recent spike in Tesla sales included ownership expansion to more mainstream consumers, many of whom are not as familiar with the ins and outs of their cars, including the purpose of—or even existence of—battery preconditioning. Elements of that new buyer base just learned the hard way that EV ownership is a little more complicated in cold weather.
Snow
In the Fox 32 footage I watched it was clear that some of the charging units were rendered inaccessible by snow. Tesla-owner message boards are dotted with driver complaints regarding inadequate snow removal at Supercharger locations. Obviously, removing one or more charging units from the mix due to inaccessibility is going to exacerbated wait times for charger access.
The O’Hare Factor
The Fox 32 report noted that several of the Tesla owners experiencing charging difficulty had just arrived in Chicago by way of O’Hare Airport. This is interesting for a number of reasons. First, by most accounts, only three of the 13 Supercharger stations in the Chicago area were affected by the meltdown: Country Club Hills, Oak Brook, and Rosemont (all Chicago suburbs).
Rosemont is adjacent to the airport, and Oak Brook is just off of a major artery which runs past O’Hare. Country Club Hills is a little more remote.
A point being made is that any EV loses about one percent of its battery charge each day it sits undriven. Of course, the rate of energy loss would increase as temperatures drop.
However, Teslas equipped with the maker’s Sentry Mode security system—which allows for, among other things, remote access to the car’s external cameras—can drain the battery by a whopping 15 percent per day, assuming the system is in use. It’s likely that a number of Tesla owners arrived back in Chicago only to learn that the extreme cold, and possible Sentry Mode use, had taken a serious toll on their states of charge.
It seems logical then that these drivers would head for the nearest/most-convenient Superchargers, Rosemont and possible Oak Brook, creating a logjam of would-be station users.
The Lithium Iron Phosphate Factor
Within the last year or so, Tesla began installing lithium iron phosphate (LiFePO4) batteries in the least-expensive versions of the Model 3 compact sedan and Model Y small crossover. Though iron-phosphate batteries are less energy dense than lithium-ion batteries, they cost less to produce, reportedly enjoy longer service lives, and are capable of charging more quickly.
Iron-phosphate batteries are also subject to greater performance loss in cold weather than lithium-ion batteries. It’s possible that the new iron-phosphate batteries are part of the problem here, however as noted earlier, Tesla cars are sold in markets where the temperatures fall below those seen this week in Chicago. That said, Tesla has been tight lipped about the markets in which it sells models equipped with the iron-phosphate batteries. So, who knows?
Final Thoughts
Now, we can’t say for certain that none of the units at the Supercharger stations in question didn’t fail, but we do know that Superchargers in rougher climates than Chicago are known to operate as expected, uncompromised—or at least not much compromised—by extreme cold.
We know, too, that plenty of Tesla vehicles ran just fine during the Chicago-area cold snap. What we are suggesting is that a large number of un-preconditioned Tesla vehicles in low states of charge descended at approximately the same time in conditions that made it very difficult for regular charging to take place. And, a lot of EV owners learned a valuable lesson the hard way.
Electric-vehicle naysayers are right about EVs and the cold: Range is an issue. It would be nice if Tesla vehicles—and indeed all electric vehicles—posted touchscreen updates regarding reduced states of charge, temperature-related battery-capacity issues, and the need for preconditioning. And, given Tesla’s propensity for over-the-air updates, it’s possible such fixes are already in the works.
Note
At the time this was published, Tesla had yet to comment on the situation in Chicago. We think it likely the company will not officially acknowledge the drama, but anything is possible. Also, while we think it unlikely, it is possible that the charging units themselves failed to operate as designed. This seems unlikely, because as we noted early, the Supercharger network is generally regarded as reliable, and operates smoothly in colder climates than Chicago.
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