On March 29, 2024, the European Commission overturned the recall of Renault Zoe : “Due to a manufacturing problem, a short circuit may occur in the high voltage battery”, informed the institution. Should we see this as a sign of reliability which tends to deteriorate over time?
Probably not for this salesman from Renault Retail Group, rightly praising a used Zoe: “The batteries are almost too robust, he explains, they could last two cars and travel well over 200,000 km. So much so that we wonder what we are going to do with all these batteries. They have small breakdowns from time to time, of course, but as far as durability is concerned…”
Words that are true, whatever brand we are interested in. Tesla, for example. 1,381 American car owners shared their battery performance data on a French-speaking forum.
According to the resulting graphs, the degradation of a Tesla battery aged 4 to 5 years varies between -3.3% (i.e. 96.7% of SOH, the residual power value of the battery) and -14. 5% for the least well preserved accumulator.
From 100,000 km traveled, all the batteries have lost at least 5% SOH, except one which, at 151,400 km, still proudly displays 95.3% SOH. Only 2 cars out of the 1381 on the forum have exceeded 200,000 km to date.
The first, at 213,952 km, still offers a capacity of 85.3%. The other, which has driven 241,379 km, announces 88.4% SOH! Data collected by the start-up My Battery Health corroborates all of this.
Tesla’s batteries, mainly but not exclusively manufactured by Panasonic, appear indestructible and insensitive to the passage of time. A Model S having traveled 288,000 km thus offers a residual capacity of 89.5%…
Harmful elements
The batteries are therefore rather solid: “The average rate of degradation is 2 to 3% per year, notes Guillaume Hébert, the director of GetMoba, until reaching 70% SOH after eight to ten years. Some batteries really don’t deteriorate quickly, others more so, it depends on how they are used.”
A report from the Atomic Energy Commission (CEA) from December 2022 indicates that “electric vehicle batteries will reach the end of their life at the same time as the vehicle they equip, i.e. after around ten years, fifteen years maximum”. Various phenomena still tend to degrade batteries.
First of all, “storage”, according to Guillaume Hébert. Leaving a car with a completely discharged battery in a park for several weeks is the perfect example of what you should not do, otherwise you risk damaging the accumulator: “When storing, you should charge the battery to 50-60% and not let it drop below 40%”continues the young entrepreneur, who also points out the harmful impact of the highway-fast charging couple on the durability of batteries.
“A battery charged normally in an hour or an hour and a half, no problem”, agrees Serge Pélissier, scientist specializing in batteries, research director at Gustave-Eiffel University. For the teacher, with frequent fast charges, “we create aging concerns which can be quite severe” due to the temperature rise of the device.
The heat would indeed be harmful to the accumulators in the long term: “A fully charged car at a temperature above 40°C leads to accelerated aging”, notes Serge Pélissier again. The Batteries project manager of the French Institute of Petroleum and New Energies (Ifpen) is even more precise and explains the so-called phenomenon of “lithium plating” : “When you charge a very dense battery cold or above 25°C but with high power, lithium in the metallic state forms on the graphite electrode”notes Julien Bernard.
This lithium, which has permanently changed state, then harms the overall capacity of the battery. The heart of electric cars is therefore not insensitive to the passage of time or charging cycles, but its reliability means that most manufacturers offer an eight-year or 160,000 km warranty on the batteries.
The majority of current electric cars have not reached this age, and are therefore still covered by their various manufacturers. Suffice it to say that trying to find out the state of health of your battery is currently not an essential concern for motorists: “According to the contacts I have had with managers of used vehicle fleets, this is not really a question that arises”smiles Cyrille Péguy, sales manager at Dekra.
Towards a health certificate?
The German specialist in automobile-related services is, however, today in a presentation phase to second-hand professionals. Dekra has a method for quickly testing an accumulator and then issuing a valid certificate of health to the vehicle: “We are carrying out a dynamic test, you have to go up to 50 km/h. The higher the resistance of the battery, the healthier it is.”indicates Mr. Péguy.
At Renault, which has proven to be a pioneer in electric cars, used vehicles do not systematically benefit from the “battery certificate” proposed by the manufacturer: “We can do it”, nevertheless agrees a salesman in a dealership, visibly surprised by a request for a part that is still guaranteed.
It could be different tomorrow. The European Commission intends to put in place a “battery passport” from 2026. This will involve affixing a QR Code to each accumulator. This will hold all the information on the device (typology, origin, capacity, etc.), but should also include data related to the maintenance carried out as well as to “operation history”, according to the Commission.
Closer to us, in France, a bill was tabled by ex-MP Dino Cinieri in June 2023. This text, which will probably never come to fruition, aimed precisely to provide clear and objective information on the state of battery health and its ability to be recharged in a given time.
Mr. Cinieri is no longer an MP today, but no matter: the seed has been planted and it will seem logical that in the future automotive professionals will all present a health check of the cars offered for sale .
Because there is an undeniable fact: a new battery costs around €17,500 on a small vehicle according to the Association for the Future of the Electro-Mobile Vehicle (Avem), and €25,000 when it is an accumulator. high capacity.
The opinion of the Auto-Journal
Battery manufacturers seem to have done a good job and everyone agrees that they age much better than expected. Their durability should not be a concern, but a question will then arise: what do we do with a car that is barely 10 years old with a battery deemed to be out of service? Even more than today, the concept of a disposable car is likely to persist.
Find our survey on the aging of automobile batteries in the Auto-Journal n°1157 of 04/18/2024.
