Electric vehicles' battery endurance: Assured for extended usage duration
For quite some time, doubts about electric cars' longevity were mainly centered around the possibly short lifespan of the battery. However, this component is now widely recognized as incredibly dependable.
In the past, the engine was the priciest part of a vehicle, with a lifespan of around 200,000 to 300,000 kilometers deemed acceptable with proper maintenance. Reliability was a crucial factor for auto buyers. But when it comes to electric vehicles, the battery holds the key to their lifespan. A malfunctioning battery can lead to a total loss, which isn't just inconvenient but also costly.
Sadly, premature battery failure isn't just a tale spun by gas enthusiasts, but a reality for some electric vehicle drivers. However, the longevity of batteries is becoming increasingly predictable, and the expected lifespan is remarkably high. In many cases, it even surpasses the car's lifespan. Credit for this goes to improved software and cell chemistry. However, the battery's health is still significantly influenced by the user and their usage pattern.
Signs: high mileage and long warranties
There are clear signs that batteries are no longer the fragile and error-prone parts they once were. For instance, used electric vehicles with high mileage are becoming common. On mobile.de, a platform for buying used cars, over 75,000 electric vehicles are listed, and around 450 of them have clocked over 150,000 kilometers. Around 150 vehicles even surpass the 200,000-kilometer mark, with some Teslas even hitting 300,000 kilometers! High mileage and electric motors are no longer mutually exclusive.
Another sign of battery reliability is the expanding warranty coverage from auto manufacturers. Initially, when electric vehicles came into mass production, the fear of battery failure often led to leasing models. In these cases, only the car was purchased, but the battery was rented on a monthly basis. If the battery degraded significantly or failed altogether, the responsibility fell on the manufacturer, not the owner.
However, today, manufacturers offer explicit and generous warranties for batteries. Their confidence in their reliability has grown with practical experience, and so have their warranty promises. A battery warranty of 8 years or 160,000 kilometers is now standard. Some manufacturers even offer 10 years or up to 250,000 kilometers of warranty. Lexus extends the warranty for the UX 300e to 10 years or 1,000,000 kilometers, a statement of confidence from the manufacturer's point of view.
Out of warranty: excessive stress
But one isn't always in the clear with warranties. If the battery is subjected to excessive stress factors, it can fall out of warranty. Deep discharging, missed servicing, or a charging behavior that heavily loads the battery could give the manufacturer valid reasons to deny warranty service. Those who want to stay on the safe side should pay close attention to the exact conditions and usage recommendations associated with the warranty.
The warranty case isn't limited to when the battery fails completely, but also when its charging capacity drops below a certain level. The State of Health (SoH) value, which indicates the percentage of the original capacity still available, provides information about this. If the capacity falls below about 80 percent (in some cases, the warranty limit is 70 percent) of the original storage capacity during the warranty period, the warranty case applies. If there's only 79 percent left, the battery is not defective, but the range has significantly decreased. While this may not affect long-range cars, it can create an annoying restriction for city cars with small batteries.
Factors affecting SoH
Several factors influence the SoH. Time plays a role due to chemical decomposition processes in the anode and cathode. Besides this 'calendar aging', the number of charging cycles is likely the most significant aging factor. With each charge, a part of the capacity is lost.
In lithium-ion batteries, it's assumed that the capacity won't fall below 80 percent after more than 1,000 complete charging cycles. This figure is impressive, considering an average electric vehicle range in 2023 of around 400 kilometers, which would theoretically enable a mileage of 400,000 kilometers, roughly calculated and without considering dynamic degradation.
However, this is a theoretical value, as a battery's degradation is influenced by additional factors dependent on the individual user behavior. Those who drive aggressively will put more strain on the battery, as it's thermally stressed more at high power consumption. Extreme outdoor temperatures can also impact battery cells. Those who store their electric car in a consistently climate-controlled garage and not in the blazing sun or on frosty days outside will slow down the battery's degradation curve.
Charging behavior plays a significant role
Charging behavior also has a massive impact. Frequent refueling at fast-charging stations will cause the degradation curve to move down the time axis more quickly, as fast charging also means thermal stress for the energy storage. On the other hand, slow and gentle AC charging overnight at a home charging station will slow down the battery's aging, as shown by laboratory tests on the cell level and real-life examples of electric car users. This doesn't mean rapid charging stations should be avoided, but their frequent use will only slightly impact the long-term SoH development throughout the battery's entire aging process.
The charging level of a battery, often referred to as the State of Charge (SoC), significantly impacts its lifespan. Regularly draining the battery, resulting in frequent SoC levels close to 0%, followed by full recharges (SoC of 100%), accelerates battery aging. Maintaining a moderate charging condition, such as partial charging within the 60-80% range, can extend the battery's life by up to five times, according to experts. In real-world scenarios, a SoC range between 20-80% is more suitable.
Recent findings by YouTuber and scientist "Akkudoktor" Andreas Schmitz, reveal contrasting instances of electric vehicle battery degradation. A Norway-based Tesla Model 3 taxicab with frequent high-speed charging (93% rate) reached a critical State of Health (SoH) of 80% after approximately 110,000 kilometers. In stark contrast, a Tesla Model S P90 driven over 2 million kilometers by Hansjoerg-Eberhard Freiherr von Gemmingen-Hornberg, had multiple battery replacements, with each battery averaging a lifespan of around 500,000 kilometers.
These examples depict a significant disparity in battery lifespans. Schmitz aimed to discover the average distance required to achieve an SoH of 80%, through data collected from the community and forums. The calculated outcome is about 250,000 to 300,000 kilometers with regular use, given current technology. The use of alternative cell chemistries like Nickel-Mangan-Cobalt (NMC), Sodium-Ion (Na-Ion), and particularly Lithium-Iron-Phosphate (LFP) is acknowledged for their exceptional cycle life and expected to deliver higher ranges in the future. Chinese company Svolt projects over 2,500 charge cycles and over one million kilometers for their upcoming Short-Blade battery (LFP).
Battery-beneficial driving habits
Motorists who follow battery-friendly driving habits are likely to enjoy a boosted range and potentially a higher resale value. The demand for battery certificates, providing information on SoH, is expected to rise in the used car market. A high SoH value grants sellers a stronger bargaining position, leading to increased prices. However, as the used electric vehicle market gains economic importance, battery certificate fraud may emerge as an alluring business model.
This trend also pertains to battery retrofits. A severely degraded vehicle battery is not necessarily the end of its electric life. Numerous providers now offer retrofit solutions, replacing aging batteries in older electric vehicles with new ones. Mandrill Automotive from Göppingen, for instance, caters to the BMW i3. A new 120 Ah storage unit, priced at around 13,600 euros, boasts enhanced capacity compared to the original 60 or 94 Ah versions. According to "Auto Motor & Sport", Mandrill is developing a new battery format with different cells and chemistry, which may extend the i3's range to 400 kilometers. Currently, the battery redesign for the i3 comes with a 10-year warranty.
Practically, battery lifespans will be more prolonged. Batteries discarded from electric vehicles do not immediately head to the scrapyard but are repurposed for stationary energy storage, such as solar power storage, and can maintain operation for an additional ten years.
Despite initial concerns about the longevity of electric cars' batteries, their reliability has significantly improved. Today, used electric vehicles with high mileage are becoming common, and battery warranties from manufacturers have expanded, reflecting their confidence in battery reliability.
With electric vehicles, maintaining the battery's health and charging behavior plays a significant role in extending its lifespan. Consistently charging the battery between 60-80% and avoiding frequent fast-charging can help slow down the battery's degradation.
