Aviloo's 500,000 Battery Tests Expose the Used-EV Lottery

Austrian battery diagnostics firm Aviloo evaluated more than 500,000 battery tests and found that capacity loss in used electric-vehicle traction batteries varies widely between vehicles, leading the company to recommend a manufacturer-independent battery test before any used-EV purchase.

The single most expensive component in a used electric car is the one buyers cannot see, cannot easily test at the kerbside, and cannot replace cheaply if it disappoints. New evidence suggests that component is also the least predictable part of the deal.

Aviloo, the Austrian battery-diagnostics specialist, has evaluated more than 500,000 battery tests and found that the capacity loss of used traction batteries — the large packs that drive the wheels, as distinct from the small 12-volt battery that runs the lights and electronics — varies significantly from vehicle to vehicle. The company's conclusion is blunt: a manufacturer-independent battery test should come before any purchase decision, not after it.

Why an average degradation figure tells a buyer almost nothing

Used-EV batteries have carried an undeserved reputation for years. The popular assumption, inherited from smartphones and early hybrids, is that packs decay steadily and predictably, so that a car's age and mileage should be enough to estimate what is left. Fleet averages published by manufacturers and analysts have generally supported the optimistic version of that story: degradation, on average, is modest.

The trouble is that no buyer purchases an average. They buy one car, with one pack, that has lived one particular life. Aviloo's dataset — drawn from more than half a million individual tests — points to wide dispersion around whatever the mean happens to be. Two cars of the same model year, with similar odometer readings and similar asking prices, can arrive at the forecourt with materially different amounts of usable energy left in them.

That dispersion is not mysterious. Battery ageing is driven by a stack of variables that never appear in a classified listing: how often the car was fast-charged, whether it was routinely parked at a high state of charge, how hot or cold the climate was, how the thermal management system was maintained, how much of the mileage was towing or motorway cruising versus gentle urban running, and how long the vehicle sat unused. A pack that spent three years shuttling between rapid chargers on a ride-hail rotation is not the same asset as one that trickle-charged overnight in a suburban garage, even if the two cars are twins on paper.

What an independent test changes in a negotiation

Aviloo's business is measuring precisely that, independently of the carmaker. The distinction matters. A vehicle's own dashboard state-of-health readout, where one is offered at all, is generated by the manufacturer's own battery management software, using proprietary methods that differ between brands and are not designed as a resale valuation tool. Buyers have no way to compare a figure from one brand against a figure from another, and no way to audit either.

An independent measurement converts an unknown into a number that both sides of a transaction can argue about. That is the real commercial function here. If degradation genuinely varies widely across otherwise comparable cars, then a market that prices used EVs mainly on age, mileage and trim is systematically mispricing a large share of them — overpaying for the tired examples and underpaying for the healthy ones. Testing is the mechanism that lets the price discriminate.

For the seller of a well-kept car, that cuts in their favour. Certified battery health is a document that justifies asking above the model's book value, in the same way a full service history does for a combustion car. For the buyer, it is downside insurance on the component that dominates the vehicle's replacement cost. As electrive reported, the recommendation from Aviloo's evaluation is that this test precede the purchase decision — the sequencing is the point, because after money changes hands the information has no leverage value.

Residual values, leasing books and the trade-in desk

The implications run well past private buyers. Residual value — what a vehicle is assumed to be worth at the end of a lease — is the number that sets monthly leasing payments, and getting it wrong is expensive for whoever holds the risk. Leasing companies, captive finance arms and rental fleets have written billions of euros and dollars of EV residuals on assumptions built from model-level averages. If the true distribution around those averages is wide, the risk is not that the average is wrong but that the tails are fatter than the models assume, leaving a meaningful slice of returning vehicles worth appreciably less than the book says.

Wide dispersion also creates an adverse-selection problem familiar from every used-goods market. If sellers know more about their car's condition than buyers do, buyers rationally discount everything, healthy cars get withheld from sale, and the average quality on offer falls further. Cheap, standardised, independent testing is the classic remedy: it lets good cars prove they are good, which supports prices across the segment rather than dragging them down.

Remarketing operations, auction platforms and dealer trade-in desks are therefore the natural adopters. A battery certificate attached to a listing does for EVs roughly what an emissions and mechanical inspection does elsewhere — it standardises the information, narrows the bid-ask spread and speeds up turnover.

What to watch from here

Three things will determine whether independent testing becomes routine rather than niche. The first is regulation: battery state-of-health disclosure requirements, wherever they are adopted, would move testing from optional to mandatory overnight and hand a substantial market to whoever can perform the measurement at scale. The second is insurance and warranty pricing, which needs exactly this kind of dispersion data to underwrite battery cover sensibly. The third is second-life and recycling demand — a pack retired from a car is worth more as stationary storage if its remaining capacity is documented rather than guessed.

The broader equity market gave no particular signal on any of this during the session in which the findings circulated. The S&P 500 tracker SPY traded at $764.96, up 0.42% on the day, with the Nasdaq 100 proxy QQQ at $708.54, up 0.13%, as of 17:45 GMT on 2 September 2026. Battery diagnostics remains a small, largely private corner of the electrification supply chain.

For anyone shopping the used-EV lots in the meantime, the practical takeaway from half a million tests is simple enough. Age and mileage are a starting point, not an answer. The pack is the asset, and the only way to know what is left of it is to measure it — before signing, not after.

Key facts

• Battery tests evaluated: More than 500,000, by Aviloo
• Core finding: Capacity loss in used traction batteries varies widely between vehicles
• Aviloo's recommendation: A manufacturer-independent battery test before any purchase decision
• Market backdrop: SPY $764.96 (+0.42%), QQQ $708.54 (+0.13%) as of 17:45 GMT, 2 Sept 2026

Frequently asked questions

What did Aviloo actually find?

Aviloo evaluated more than 500,000 battery tests and found that the capacity loss of used electric-vehicle traction batteries varies significantly from car to car. The company's conclusion is that a used EV's battery condition cannot be reliably inferred from age and mileage alone, and that an independent test should precede any purchase decision.

What is a traction battery?

The traction battery is the large high-voltage pack that stores energy and drives an electric vehicle's motor. It is separate from the small 12-volt battery that powers lights, infotainment and electronics. The traction pack is typically the single most expensive component in an EV, which is why its remaining capacity dominates the car's resale value.

Why not just use the car's own state-of-health display?

On-board readings are produced by the manufacturer's own battery management software using proprietary methods that differ between brands. That makes figures hard to compare across makes and impossible for a buyer to audit. An independent test provides a measurement generated outside the carmaker's system, which is the reason Aviloo recommends one.

What causes two identical EVs to age differently?

Battery ageing depends on how the car was used rather than just how far it travelled: frequency of rapid charging, how often it sat at a high state of charge, ambient temperature and climate, thermal-system condition, the mix of motorway versus urban driving, towing loads, and long periods of inactivity. None of these appear in a typical used listing.

How does this affect leasing and residual values?

Residual value assumptions set monthly leasing payments. Those assumptions are usually built from model-level averages. If real-world degradation is widely dispersed around the average, a meaningful share of returning vehicles will be worth less than the book assumes, concentrating losses with whoever holds the residual risk — leasing companies, captive finance arms and fleets.

Does a battery test help sellers as well as buyers?

Yes. For a well-maintained car, a certified battery health measurement functions like a full service history: documentary evidence that justifies asking above book value. Without it, buyers rationally discount every vehicle to account for the possibility of a degraded pack, which penalises owners of healthy cars alongside everyone else.

Sources

• Battery health of used EVs varies significantly — electrive

Photo: Jose Ricardo Barraza Morachis · Pexels Licence — source