Electric cars can safely charge quickly, but range still dips at high speeds
The good news is that most electric car owners don’t have to worry that repeated fast charging while driving long distances will damage the battery; unfortunately, the problem of chronic range depreciation due to prolonged high-speed highway cruising doesn’t go away.
A recent article in the Financial Times aired the problem of a Nissan Leaf driver who used fast chargers on the highway up to 4 times a day, with disastrous consequences for the battery. It was an unfortunate penalty for Nissan’s early lead in developing battery power. Its choice of air-cooled technology doesn’t seem to be an issue for most of the latest battery-only sedans and SUVs.
Professor David Greenwood of Britain’s University of Warwick points out that the Leaf’s design, with a relatively small and inexpensive battery, makes it ideal for on the go. Its limited cooling capacity, however, makes it susceptible to overheating and multiple fast charging, unlike the battery technology of more expensive vehicles like Teslas or the Jaguar I-Pace with active battery cooling which can easily handle fast charging. .
But a damaging flaw for electric cars remains high-speed cruising, the problem that dare not speak its name. I have yet to read from a manufacturer that there could be a substantial range penalty for prolonged legal cruising in the fast lane in an electric car, although there are many claims that sometimes exaggerate the battery capacity over 30%.
British expert Nick Molden, managing director of Emissions Analytics, agrees that cruise speeds quoted at 80mph, the norm in Britain, generate significant range penalties.
Most potential electric car buyers are unaware that as soon as they regularly increase their speed above 60 mph the range starts to run out, and in mainland Europe often with a 130 mph speed limit km/h (81.25 mph), it will disappear at an alarming rate. In Britain the speed limit is 70mph on the motorways, and in the real world that becomes around 80mph indicated and no doubt a similar leeway is practiced in Europe, except in Germany of course where many large chunks of the freeway system do not. have a speed limit at all.
My own data shows that most modern electric cars, driven on highways at speeds close to 75 mph, will lose range by just over 30% of the available range offered. In other words, if range availability is 100 miles, don’t expect to go much further than around 65 miles. Some models like the 62kWh Nissan Leaf, 42kWh Fiat 500e, 50kWh Vauxhall Corsa and 78kWh Polestar 2 won’t get you 50% of the way there.
Professor Greenwood points out that electric car drivers operate in varying conditions which generate different performance, while hot or cold climates can adversely affect performance.
“Electric cars are much more energy efficient than ICEs (internal combustion engines), and this efficiency is relatively constant across the entire operating range. This means range will be much lower at high speeds than at low speeds. speed – simply because it takes more energy per mile at high speeds than at low speeds due to the car’s aerodynamic drag increasing with rapidity,” Greenwood said in an email exchange.
“This is masked a bit by ICE engines as they are very inefficient at low speeds – so although the car’s power requirements are lower, the inefficiency of the engine means the gas mileage isn’t all that different from which it is at high speeds where the drag is higher but the engine is a bit more efficient,” Greenwood said.
I asked some automakers what advice they give electric car buyers.
Nissan said European Leafs come with an 8-year/100,000-mile warranty and most buyers bill door-to-door. Frequent use of high-speed chargers should be avoided. Is the standard instruction to try not to exceed 80%, never drop below 20%, ideally fill to 50%?
“We do not recognize this advice,” Nissan said. Recharging to 100% before a long ride is fine.
Volkswagen recommended avoiding routine quick-charges, but driving long distances with lots of quick-charges was no problem. The VW warranty is 8 years or 160,000 kilometers (100,000 miles). VW recommends regular charging not exceeding 80%, this capacity should not drop below 20% for too long, while fast charging should stop at 80%.
Hyundai said there are no restrictions on repeated fast charging. The optimal charge is between 10 and 80%, but there was no technical reason not to charge to 100%.
“There is a buffer on the battery storage anyway and therefore a slight difference between what the driver sees as a percentage of charge and the actual amount in the battery, i.e. the level of usable battery that the driver sees may be 100% but the actual battery charge level may be slightly lower,” Hyundai said in a statement.
No warning about mileage deprivation of the fast lane.
According to LMC Automotive analyst Oliver Petschenyk, most manufacturers use liquid cooling for longer runs, while Tesla has added its own adjustment.
“Tesla, for example, has a ‘road trip’ user case that exactly covers high-speed travel with boost along the route. Tesla accelerates boost speed based on battery temperature, but what’s interesting is that it minimizes battery degradation by preheating the battery before boosting I think a lot of EVs don’t have this feature, fast charging a cold battery is the worst battery degradation scenario via dendrite formation Tesla is constantly refining thermal management and charger settings to maximize customer experience and minimize battery degradation and apply them to customer vehicles,” said Petschenyk.
Emissions Analytics’ Molden, pointing to the typical 8-year battery warranty, said there was still little evidence that this was a reliable warranty, and if it wasn’t, there would be heavy penalties for manufacturers.
“If the batteries last less than 8 years, the manufacturers will rack up a huge liability if they don’t. Will they last much longer than that? 10 years. It makes a huge difference to the decarbonization effort,” Molden said.
Molden said the CO2 benefits of electric cars would not be much at 50,000 miles, but at 100,000 the calculations would be more favourable.
“Battery life really matters,” he said.
Molden pointed out that the damping calculations could be overwhelmingly favorable to the ICE power supply if battery life was in question. The cost of a replacement battery was so high that a write-off might be the smart move in a battery-powered car, while an older ICE might be in working order at a modest cost.
Some analysts believe that manufacturers mask gradual battery deterioration by allowing the system to display, say, 10% less than reality at first, and then slowly allowing it to catch up to reality. This would make the battery life good and then it would degrade very quickly, but this is currently just a theory.
There are differing views on how best to deal with the battery, and Professor Greenwood from the University of Warwick calls for flexibility.
“The recommendation to avoid charging more than 80% is to prolong battery life – batteries age faster if kept at 100% charge for long periods of time, and especially in hot weather, so if you don’t need the full range of the vehicle that day, it’s best to only charge to 80-85%,” Greenwood said.
“This shouldn’t discourage you from fully charging the car when you have to go on long drives and need the full range, as the battery won’t stay above 85% charge for very long under these circumstances – maybe just an hour or two The problem is really where people leave the car permanently connected to a charger, and it stays fully charged for days or weeks at a time. of the battery at very low charge, less than 5%, especially if you then quickly charge it in very cold conditions,” he said.