Heavy use of fast charging may accelerate the degradation of electric vehicle batteries, but that does not mean they are damaged as soon as they are connected to a high-power charger. The scale of the effect depends on the charging rate, temperature and battery chemistry, as well as the efficiency of the systems managing cell temperature and charging power. Direct-current fast charging allows some vehicles to raise their battery level from about 10% to 80% in 15 to 45 minutes.
Its power starts at tens of kilowatts and can reach 350 kilowatts or more at ultra-fast stations, compared with about 1.4 to 1.9 kilowatts for Level 1 home charging and usually up to about 22 kilowatts for Level 2. The higher currents place battery cells under greater stress than slower charging.
During charging, lithium ions move to the negative electrode and settle into its structure. But applying a high current, especially when the battery is cold or nearly full, may cause the ions to arrive faster than the electrode can accommodate them. In that case, lithium can deposit on the electrode’s surface in metallic form, in a phenomenon known as “lithium plating.”
Lithium plating explains the strain caused by high charging rates
Research published in the Journal of Power Sources linked high-rate charging to a greater likelihood of this phenomenon, along with thermal stress and increased internal resistance, factors that may accelerate cell degradation. These effects do not occur to the same degree during every fast-charging session.
Battery management systems in modern cars monitor temperature and state of charge, automatically reducing power when conditions become unsuitable. Temperature plays a central role in the rate of degradation because fast charging generates more heat as higher currents pass through the battery.
Thermal management limits cell degradation
By contrast, ion movement inside the battery slows in cold weather, increasing the likelihood of lithium deposition when it is charged at a high rate. For this reason, modern cars raise the battery temperature to a suitable range before reaching a charging station. An analysis by Geotab covering more than 22,700 electric vehicles from 21 models found that average battery capacity degradation was about 2.3% annually.
Nevertheless, the analysis concluded that modern batteries remain generally durable and can often last beyond the vehicle’s typical service life. Their ability to withstand fast charging varies according to battery chemistry.
Different battery chemistries alter their ability to withstand use
In tests conducted by researchers at Carnegie Mellon University, lithium iron phosphate batteries, or LFP, were the most durable and showed no significant increase in degradation even when fast charging accounted for more than 90% of sessions. Nickel-manganese-cobalt, or NMC, batteries maintained good life in most scenarios before their degradation accelerated when they relied almost entirely on fast charging.
Nickel-cobalt-aluminum, or NCA, batteries were the most sensitive, with degradation increasing clearly as the share of fast charging rose. The study converted the degradation results into a model of battery replacement costs through the point at which the vehicle reached 150,000 miles, or about 241,000 kilometers.
Replacement costs vary among different battery chemistries
In an extreme test scenario combining more than 90% fast charging with use of the battery’s full voltage range, the estimated cumulative cost was zero for LFP batteries, about 27 thousand dollars for NMC batteries and as much as 210 thousand dollars for NCA batteries.
These estimates do not represent actual repair bills, but modeling results based on cells subjected to charging cycles under specific conditions. When fast charging was limited to a range of about 20% to 80%, the estimated cost fell to zero for NMC batteries and about 63 thousand dollars for NCA batteries. Protecting the battery does not always require strict adherence to the 20% to 80% range.
The Geotab analysis showed that the notable effect of extreme charge levels appears when the vehicle spends more than 80% of its time at very high or very low levels. Thus, charging the battery to 100% before a long journey, or occasionally letting it fall below 20%, does not mean it will be damaged.
Alternating-current charging at home or work remains less stressful for the battery in daily use, while fast charging can be reserved for long journeys or situations requiring shorter waiting times. It is preferable not to leave the vehicle completely full or nearly empty for long periods, while following the charging limits set by the manufacturer for each battery type.
In hot weather, avoiding ultra-fast charging immediately after driving that has raised the battery temperature, when waiting is possible, helps reduce thermal stress.
In extreme cold, preparing the battery before charging becomes more important. In some vehicles, this process can be activated automatically when a fast-charging station is entered as a destination in the navigation system.
