Electric Cars Can Fast-Charge Safely, But Range Still Dives At Speed

Electric Cars Can Fast-Charge Safely, But Range Still Dives At Speed

The good news is most electric car owners don’t have to worry that repeated fast charging during long-distance driving will damage the battery; unfortunately the problem with chronic range depreciation from prolonged high-speed highway cruising isn’t going away.

A recent article in the Financial Times aired the issue of a Nissan Leaf driver who used highway fast-chargers up to 4 times a day with dire consequences for the battery. This was an unfortunate penalty for Nissan’s early lead in the development of battery power. Its technology choice of air cooling doesn’t appear to be an issue for most of the latest battery-only sedans and SUVs.

Professor David Greenwood of Britain’s Warwick University points out that the design of the Leaf, with a relatively small and inexpensive battery, makes it ideal for commuting. Its limited cooling ability though does make it susceptible to overheating and multiple fast charging, unlike the battery technology in more expensive vehicles like Teslas or the Jaguar I-Pace with active battery cooling which can easily handle fast charging.

But a damaging shortcoming for electric cars remains high-speed cruising, the problem that dares not speak its name. I’ve yet to read from a manufacturer that there might be a substantial range penalty for prolonged legal fast-lane cruising in an electric car, although there are plenty of claims that exaggerate battery capacity sometimes by more than 30%.

British expert Nick Molden, chief executive of Emissions Analytics, agrees that indicated 80 mph cruising speeds, the norm in Britain, generate significant range penalties.

Most potential buyers of electric cars are not made aware that as soon as they consistently raise their speed over 60 mph, range begins to drain away, and in mainland Europe often with a 130 km/h (81.25 mph) speed limit it will disappear at an alarming rate. In Britain, the speed limit is 70 mph on motorways, and in the real world this becomes about an indicated 80 mph and no doubt a similar leeway is practiced in Europe, except in Germany of course where big chunks of the motorway system don’t have a speed limit at all.     

My own data shows that most modern electric cars, driven on motorways at speeds close to 75 mph, will shed range at just over 30% compared with the range availability on offer. In other words, if the range availability is 100 miles, don’t expect to go much further than about 65 miles. Some models like the Nissan Leaf 62 kWh, Fiat 500e 42 kWh, Vauxhall Corsa 50 kWh and Polestar 2 78 kWh won’t get you 50% of the way.

Professor Greenwood points out that electric car drivers operate under varying conditions which will generate different performances, while hot or cold climates can undermine performance.

“Electric cars are much more energy efficient than ICE (internal combustion engines), and that efficiency is relatively constant over the entire operating range. What this does mean is that the range will be much lower at high road speeds than it is at low road speeds – simply because it takes more energy per mile at high speed than it does at low speed due to the aerodynamic drag of the car increasing with speed,” 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 energy requirement of the car is lower, the inefficiency of the engine means that the petrol consumption is not that different to what it is at high speed where the drag is higher but the engine is a bit more efficient,” Greenwood said.

I asked some manufacturers what advice they gave to electric car buyers.

Nissan said European Leafs are guaranteed for 8 years/100,000 miles, and most buyers charge at home. Frequent use of high-speed chargers should be avoided. Is the standard instruction try not to fill past 80%, never let it drop under 20%, ideally refill at 50%?

“We do not recognize this advice,” Nissan said. Charging to 100% before a long journey is fine.

Volkswagen recommended avoiding routine fast-charging, but driving long-distances with numerous fast-charging was no problem. VW’s guarantee is 8 years or 160,000 kilometers (100,000 miles). VW recommends regular charging not exceed 80%, that capacity shouldn’t drop below 20% for too long, while fast charging should stop at 80%.

Hyundai said there are no restrictions on repeated fast charging. Optimum charging is between 10 to 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 charge and the actual amount held within the battery, i.e. the usable battery level that the driver sees may be 100% but the actual battery charge level may be slightly below,” Hyundai said in statement.

No warnings about fast lane mileage deprivation.

According to LMC Automotive analyst Oliver Petschenyk most manufacturers use liquid cooling for capable longer journeys, while Tesla has added its own tweak.

“Tesla for example has a “road trip” user case that covers exactly high-speed travel with supercharging along route. Tesla throttles supercharge speed depending on battery temperature but what’s interesting is it minimizes battery degradation by prewarming the battery before supercharging. I believe a lot of EVs do not have this function, fast charging a cold battery is the worst-case scenario for battery degradation via dendrite formation. Tesla is constantly fine-tuning the thermal management and charger settings to maximise customer experience and minimize battery degradation and applying them to customer vehicles,” Petschenyk said.

Emissions Analytics’ Molden, pointing to the typical 8-year warranty on batteries, said there was little evidence yet that this was a reliable guarantee, and if it wasn’t, there would be big penalties for manufacturers.

“If batteries last for less than 8 years, manufacturers will be storing up massive liability if they don’t. Will they last much longer than that? 10 years. It makes a huge difference to the decarbonisation effort,” Molden said.

Molden said electric car CO2 advantages wouldn’t be much at 50,000 miles but at 100,000 calculations would be more favorable.

“The lifespan of the battery really matters,” he said.

Molden pointed out that depreciation calculations could be hugely in ICE power favor if battery life was questioned. The cost of a replacement battery was so high, a write-off might be the sensible solution in a battery car, whereas an older ICE could be roadworthy at a modest cost.

Some analysts believe manufacturers mask the gradual deterioration of the battery by allowing the system to show, say, 10% less than reality at first, and then slowly allow it to catch up with reality. That would make battery life look good, then it would degrade very rapidly, but that is currently only a theory.

There are differing views about the best way to treat the battery, and Warwick University’s Professor Greenwood urges flexibility.

“The recommendation to avoid charging over 80% is around prolonging the life of the battery – batteries age more quickly if they are held 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 on that day, it’s better to only charge to 80-85%,” Greenwood said.

“That shouldn’t discourage you from fully charging the car when you do need to do long journeys and need the full range, as the battery won’t stay above 85% charge for very long under those circumstances – maybe just an hour or two. The issue is really where people leave the car continuously connected to a charger, and it stays fully charged for days or weeks at a time. The same is true for running the battery to very low charge, less than 5%, especially if you then fast charge it in very cold conditions,” he said.