EV batteries lose about 2.3% of their capacity a year, a 22,700-vehicle study found

Fleet-telematics company Geotab analysed more than 22,700 electric vehicles of 21 makes and models and found an average battery degradation rate of 2.3 percent a year. Applied steadily, that rate leaves a pack with about 81.6 percent of its original capacity after eight years. The number comes from the company’s own study of real-world driving, not from laboratory cycling, and it comes with a breakdown of what makes some batteries age faster than others.

The strongest single factor in that breakdown is charging power.

State of health, measured from the road

Degradation here means a falling state of health, defined in Geotab’s developer documentation as current battery capacity divided by original capacity. The original figure is calculated from data on other vehicles of the same make, model, year and trim, and the current figure is derived from the individual vehicle’s historical driving and charging data. The reported value is a best estimate with a 90 percent confidence interval around it, because telematics estimates capacity indirectly instead of draining the pack on a test bench.

Charlotte Argue, Geotab’s senior manager of sustainable mobility and the author of the study write-up, frames the result as reassuring: in her write-up, modern batteries are robust and built to last beyond a typical vehicle’s service life. The point of an average across 22,700 vehicles is that individual cars scatter widely around it, and an average of 2.3 percent hides a spread between owners.

DC fast charging above 100 kW as the largest stressor

Geotab’s study page identifies charging power as the dominant factor. Vehicles that frequently use DC fast charging above 100 kW degraded at up to 3.0 percent a year, compared with 1.5 percent for vehicles that mostly used lower-power charging, a twofold difference. At the faster rate the pack holds roughly 76 percent of its capacity after eight years, according to the write-up.

Battery chemistry explains the gap. Pushing current into a lithium-ion cell quickly generates heat and drives lithium to plate on the anode instead of settling in it, both of which permanently remove usable capacity. Slower charging gives the cell time to absorb energy with less strain, and the battery’s thermal system has less to dissipate.

Per the newswire copy of the study, vehicles that used fast charging for fewer than 12 percent of sessions degraded at 1.5 percent a year, while those above that share degraded at 2.5 percent. Argue’s advice for fleets, as quoted there, is to focus on balance: using the lowest charging power that still meets operational needs can make a measurable difference to long-term battery health.

Heat, mileage and the 20-to-80 rule

Climate and use come next. Vehicles in hot regions, defined in the write-up as places exceeding 25 degrees Celsius on more than 35 percent of days, degraded about 0.4 percentage points a year faster than those in mild conditions. High daily use, with more than 35 percent of charge cycles in a given period, added about 0.8 points, yet those vehicles still projected to 81.6 percent capacity after eight years, a trade-off Geotab calls worthwhile for fleet productivity.

The study also tests the popular rule of keeping a battery between 20 and 80 percent. In Geotab’s data the rule only mattered when a vehicle spent most of its time, more than 80 percent, at the extremes of charge; moderate exposure showed negligible effect, which the write-up attributes to buffers that manufacturers build into the software.

The 2.3 percent figure is also higher than an earlier Geotab study, which found 1.8 percent across fewer models. The company’s reading is that the difference reflects newer vehicles using more high-power charging and not a decline in battery quality. For a 150-mile car, an earlier Geotab tool release estimated about 17 miles of range lost over five years, quoting Matt Stevens, the company’s vice president of electric vehicles, that battery health matters because the pack is “the most expensive component in an EV.”

In practical terms, a car rated at 300 miles of range that degrades at the average rate would carry about 245 miles of range at the eight-year mark, a simple multiplication of 300 by 81.6 percent. The same car charged mostly at high power would be nearer 228 miles. Those are illustrations of the percentages and not range tests, since real range also depends on temperature, speed and load.

The eight-year figures in the write-up are projections from a steady annual rate, and the sample’s own limit is the open question: the page reports no measured results for packs at that age, so whether the loss stays linear or flattens remains to be shown by older vehicles.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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