SoH Is the New Mileage for Used EVs
For decades, the odometer reading has been the universal shorthand for a used vehicle's condition. Higher mileage means more wear, lower value, simpler trade-in calculation. Every dealer, every buyer, every valuation guide works from the same assumption: mileage equals condition.
For internal combustion vehicles, that assumption is roughly correct. Engines, transmissions, and drivetrains wear in broadly predictable ways relative to distance covered. A 100,000-mile petrol car has more wear than a 30,000-mile equivalent. Not always proportionally, but directionally reliable.
For electric vehicles, that assumption is fundamentally broken.
Why Mileage Fails for EVs
A 30,000-mile EV could have 95% battery health. Or it could have 78%. Same mileage. Same model. Same year. Completely different vehicles in terms of real-world capability and value.
Three factors make mileage an inadequate proxy for EV condition:
1. Driving Behaviour
How the vehicle was driven matters enormously. A 402-vehicle field study of identical EVs — same make, model, and battery — found that aggressive drivers consumed approximately 30 kWh per 100 km, while moderate drivers used just 16 to 18 kWh per 100 km. That is nearly double the energy consumption for the same distance.
Double the consumption means double the charging cycles over the battery's lifetime. More cycles means faster degradation. Two vehicles with identical mileage can have experienced vastly different stress levels depending entirely on driving style.
2. Temperature Conditions
Batteries degrade faster in extreme temperatures. A vehicle that spent three years in the south of Spain, regularly parked in direct sunlight at 40 degrees, will have aged differently from the same model kept in a temperate UK garage.
Cold extremes also cause stress. Repeated deep cold starts without preconditioning, winter commutes drawing heavily on cabin heating — these patterns accelerate degradation in ways that mileage cannot capture.
3. Charging Practices
A vehicle that was predominantly charged overnight on a 7 kW home wallbox has experienced far less battery stress than one that relied heavily on 150 kW DC rapid chargers. Fast charging generates more heat, pushes higher currents, and — over thousands of cycles — contributes to measurably faster capacity loss.
The owner's charging habits are invisible at point of sale. The mileage is the same. The battery condition is not.
The Measurement Problem
Traditional valuation tools — CAP, Glass's, Auto Trader — still primarily use mileage, age, and specification to generate trade-in and retail values for EVs. This is not because mileage is the right metric. It is because, until recently, there was no scalable way to measure what actually matters.
State of Health — SoH — is the metric that replaces mileage for EVs. It represents the battery's current maximum capacity as a percentage of its original capacity. A battery at 90% SoH can store and deliver 90% of the energy it could when new.
But not all SoH measurements are equal. As we explored in our guide to why not all SoH readings are the same, the SoH figure shown on a vehicle's dashboard is often the manufacturer's own estimate, calculated using proprietary algorithms that may not reflect true cell-level condition. An independent, TUV-certified measurement based on extractable energy in kWh provides a manufacturer-independent, comparable figure across all makes and models.
The Valuation Gap
This is where the commercial opportunity sits for dealers.
If the market is still pricing used EVs primarily on mileage, and you know the actual State of Health, you have an information advantage. That advantage works in two directions:
Buying Smarter
When sourcing stock — whether through part-exchange, auction, or trade — a vehicle with below-average SoH for its mileage is overpriced by the market. A vehicle with above-average SoH is underpriced. Without testing, you are guessing. With testing, you are making informed purchasing decisions.
A 3-year-old EV with 25,000 miles and 92% SoH is a different commercial proposition from the same vehicle at 81% SoH. The first is a strong retail unit. The second may need a price adjustment, a disclosure conversation, or a decision not to retail at all.
The difference in value between those two vehicles is significant. As we covered in the test that adds up to £900 per vehicle, a certified battery health report enables price uplifts of £450 to £900 per unit — because it provides the evidence that justifies a premium.
Selling with Confidence
When listing a vehicle with a strong SoH, leading with that data in your listing attracts a different calibre of buyer. Used EV buyers are increasingly informed. 88% want battery health data before committing to a purchase. They know mileage is not enough.
A listing that says "28,000 miles, 94% battery health certified by independent TUV-approved test" communicates something that "28,000 miles, full service history" does not. It says: we have tested this vehicle, we know what we are selling, and we stand behind it.
Buyers searching for "EV battery health" or "battery state of health" online are already looking for this information. The dealers who provide it in their listings capture that demand. Those who do not are invisible to these buyers.
SoH as the Standard
The shift from mileage to SoH as the primary valuation metric for used EVs is not speculative. It is already happening.
The EU Battery Passport regulation, arriving in February 2027, will require standardised battery health data for all new EVs. The infrastructure for battery health reporting is being built at a regulatory level. The used market will follow, because buyers will come to expect the same transparency for second-hand vehicles that they see on new ones.
In the UK, the Consumer Rights Act 2015 already creates liability exposure for dealers selling EVs with undisclosed battery degradation. If a vehicle's battery is significantly below reasonable expectations and the dealer had no evidence of its condition at point of sale, the reversed burden of proof in the first six months puts the risk squarely on the dealer.
Average dispute costs for battery-related claims run to £6,193. Battery replacement costs range from £12,000 to £25,000 or more. Testing costs approximately £35.
The arithmetic is not complicated.
The Listing Advantage
Consider two Auto Trader listings for the same vehicle — a 2023 Hyundai Ioniq 5 with 22,000 miles:
Listing A: "2023 Ioniq 5 Ultimate, 22,000 miles, full service history, one owner, excellent condition."
Listing B: "2023 Ioniq 5 Ultimate, 22,000 miles, 94% battery health certified (independent TUV-approved test), full service history, one owner, battery health certificate included."
Listing B answers the question that every informed EV buyer is asking before they pick up the phone. It eliminates the biggest unknown. And it justifies a higher asking price because it provides evidence, not just a claim.
Dealers who are already doing this report faster time-to-sale and fewer price negotiations on EVs with strong SoH results. The certificate removes the buyer's leverage to negotiate down based on battery uncertainty — because there is no uncertainty.
Making the Transition
For dealers already selling used EVs, integrating SoH testing into your stock preparation process is straightforward:
- Test every EV at point of intake — whether part-exchange, auction purchase, or trade
- Use the SoH data in your buying decisions — adjust offers based on actual battery condition, not just mileage
- Lead with SoH in your listings — make battery health data the headline, not a footnote
- Provide the certificate to every buyer — physical or digital, it becomes part of the vehicle's documentation
- Train your sales team — they should be able to explain SoH as confidently as they discuss mileage and service history
The test takes 3 minutes via an OBD-2 connection. The certificate is issued immediately. No specialist training required.
Mileage had its era. For used EVs, that era is ending. The dealers who recognise this first will set the standard that the rest of the market follows.