{"id":17233,"date":"2026-09-05T09:04:47","date_gmt":"2026-09-05T07:04:47","guid":{"rendered":"https:\/\/www.car-shooters.com\/en\/2026\/09\/05\/the-battery-of-electric-cars-how-its-made-and-how-it-ages\/"},"modified":"2026-09-05T09:04:47","modified_gmt":"2026-09-05T07:04:47","slug":"the-battery-of-electric-cars-how-its-made-and-how-it-ages","status":"publish","type":"post","link":"https:\/\/www.car-shooters.com\/en\/2026\/09\/05\/the-battery-of-electric-cars-how-its-made-and-how-it-ages\/","title":{"rendered":"The Battery of Electric Cars: How It’s Made and How It Ages"},"content":{"rendered":"

Among the cars we test on Car-Shooters, a growing number — the Tesla Model S<\/strong>, the Polestar<\/strong>, the Hyundai IONIQ<\/strong>, the Volkswagen ID. Buzz<\/strong>, the Volvo XC40 P8<\/strong> — share the same organ under the floor: a battery pack that is, by cost and by complexity, the single most important component of an electric car. Yet for most owners it remains a black box, understood only through two numbers on a screen: range, and an increasingly anxious question — how much has it aged?<\/p>\n

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From cell to pack<\/h2>\n

An EV battery is built in three layers. The base unit is the cell<\/strong>, a sealed pouch, prismatic can or cylindrical can containing two electrodes separated by a porous membrane soaked in liquid electrolyte. Most cells on the road today use one of two lithium-ion chemistries: NMC<\/strong> (nickel-manganese-cobalt), which favours energy density and is common on premium and long-range models, and LFP<\/strong> (lithium-iron-phosphate), which trades some density for lower cost, better thermal stability and longer cycle life — the reason it now equips a growing share of standard-range EVs.<\/p>\n

Cells are grouped into modules<\/strong>, wired in series and parallel to reach the working voltage (typically 350-800V), and modules are assembled into the pack<\/strong>, a sealed structural unit that today often doubles as part of the car’s floor and chassis stiffness. Around the cells sits the part that actually decides how the battery behaves and ages: the Battery Management System (BMS)<\/strong>, which measures voltage and temperature of every module, balances charge between cells, and enforces the safety limits the chemistry can’t enforce on its own.<\/p>\n

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How a battery actually ages<\/h2>\n

Unlike a mechanical part that wears out through friction, a lithium-ion cell ages through chemistry, along two parallel paths. Calendar ageing<\/strong> happens simply with the passing of time, driven mainly by temperature and by the state of charge at which the battery sits idle: a passivation layer called the SEI<\/strong> (solid electrolyte interphase) slowly and irreversibly thickens on the negative electrode, consuming usable lithium. Cycle ageing<\/strong> instead depends on use: how deep the charge\/discharge swings are, how fast the current is (notably during DC fast charging), and how hot the cells get while working. Push any of these too far — charging at very high power in already-hot conditions, for instance — and a faster, more damaging mechanism called lithium plating<\/strong> can appear, depositing metallic lithium instead of intercalating it, which both eats capacity and can create safety risks.<\/p>\n

The result is capacity fade (a fully charged pack simply holds less energy than when new) and power fade (internal resistance rises, so the same current produces a bigger voltage drop, which shows up as reduced fast-charging speed and acceleration). Most manufacturers warranty the pack down to 70-80% of original capacity<\/strong> over 8 years or ~160,000 km — a threshold, not a cliff: a battery below it still works, just with reduced range.<\/p>\n

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State of Health: a number harder to pin down than it looks<\/h2>\n

The industry calls the ageing indicator State of Health (SoH)<\/strong>, usually expressed as the percentage of original capacity still available. The problem is that SoH cannot be read directly the way a fuel gauge reads a tank: it has to be inferred, and every carmaker’s BMS infers it with its own proprietary algorithm, from voltage curves, coulomb counting and internal resistance estimates gathered during ordinary driving. A 2025 review published in npj Clean Energy<\/em> made the point explicit, calling for a standardised SoH measurement procedure for EV battery packs and proposing energy- and capacity-based metrics precisely because today no such standard exists<\/strong> at the vehicle level — which is also why the SoH percentage shown by two different EVs, or even by two apps on the same car, can disagree.<\/p>\n

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The metrology angle: measuring ageing is a research problem, not just an engineering one<\/h2>\n

Getting a trustworthy, comparable SoH number is, at its root, a metrology<\/strong> challenge — the science of measurement itself — and it is exactly what a cluster of EU-funded projects under the European Partnership on Metrology<\/strong> (coordinated by EURAMET, the network of Europe’s national metrology institutes, together with the EU’s Horizon Europe programme) has been working on:<\/p>\n