Electric car batteries: what loss of capacity and autonomy can you expect over time?

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The life of batteries in electric cars is often the subject of debate. A new study reveals the average capacity losses incurred over the years by the main smart health connected models on the market. The results are nuanced.

After only five years, electric and plug-in hybrid vehicles (PHEV) would lose an average of 10% of their battery capacity, and therefore of their electric range. This conclusion is the result of a Geotab study, offering fleet management solutions, which studied SOH (state of health, or state of health that expresses the capacity of a battery compared to its initial capacity) of the batteries of 6,300 electric and hybrid cars rechargeable over time.

The data collected show significant differences between the twenty-one models listed. For example, after four years, the average SOH of the 2005 Nissan Leaf studied is 85.7%, compared to 91.8% for Tesla Model S of the same year.

Generally, electric car batteries are guaranteed up to eight years or 160,000 km for a minimum SOH of 70%, but this varies depending on the model. The rental contract for Renault electric vehicle batteries ensures their replacement if their capacity drops below 75% of their initial capacity (60% for the Kangoo Z.E. 22 kWh).

The production of batteries is expensive and polluting and their lifespan is crucial. In view of the cost of the repairs involved, most of the faulty batteries that are no longer covered by their warranty will probably not be replaced, leaving vehicles unsuitable. Packs whose SOH is too low to meet the needs of a vehicle are not necessarily to be thrown away since they can have a second life. However, the short battery life remains a problem in itself. Fortunately, the good performance over time of the batteries of some models indicates that improvements are achievable.

What are the factors influencing the degradation of SOH?

Lithium-ion batteries are the standard in the electric car today, but not all are the same. The composition of their cathodes can vary, for example, as can their lifespan.

Recommended item: Electric cars: update on all battery technology

While battery technology plays an indisputable role in their lifespan, many other factors and good practices can influence their wear. We note for example the frequent use of fast chargers (DC) which can accelerate the degradation of SOH.

Another important concept, buffers (difference between the total capacity of a battery and its useful capacity) are unexploited areas of a battery that limit its wear. The more important they are, the more they reduce the risk of damaging cells.

Manufacturers are adopting different policies. Some people block a significant part of the batteries of their electric cars, even if it means lowering the buffers thereafter. Others, like Tesla, prefer to limit these buffer zones to the bare minimum, while encouraging their customers not to regularly charge their battery beyond a certain threshold. This allows the brand to advertise greater maximum autonomy by offering more flexibility to its customers who will occasionally be able to charge their battery at a higher SOC. This strategy nevertheless requires the brand to educate its customers about the wear and tear of their batteries.

The buffers constitute a parameter in the hand of the manufacturers, but also of the users. Indeed, Tesla is not the only brand to offer to manually limit the maximum charge level of its batteries. It is therefore preferable not to fully charge your car, unless it is necessary. Ideally, it is best to stay between 20 and 80% of charge as often as possible and this rule also applies to cars that remain parked for a long time.

If electric cars tend to see their autonomy significantly decrease in winter, high temperatures are not their friends either. Geotab has measured a twice as rapid drop in the SOH of batteries for cars with a warm climate (more than five days a year above 27 ° C) compared to those with a temperate climate (less than five days per year above 27 ° C or below -5 ° C). This difference was highlighted by comparing vehicles that have never been smart health connected to fast chargers, so the SOH is better preserved.

Finally, the battery cooling system also plays an important role. Vehicles with a liquid-cooled system therefore seem to be more resistant to time.

Logically, the more vehicles are used, the more these factors should accelerate the decrease in their SOH. Indeed, they will logically experience more charge and discharge cycles. However, according to the report published by Geotab, the impact of this factor is not so significant.

Be careful though, these results again come from vehicles not undergoing rapid charges. The latter will certainly be much more frequent for vehicles traveling the most kilometers and the difference in SOH noted according to the mileage will then be amplified. This graph is still reassuring, especially for cars that are inefficient or equipped with small batteries, which will inevitably require more charge / discharge cycles to cover a given distance. In addition, these results show that, well studied, the V2G bidirectional charge can be democratized without fear for batteries which will experience many charge / discharge cycles.

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