As we move through 2026, the UK’s used car market is reaching a tipping point. With the first massive wave of “Generation 2” electric vehicles now hitting the second-hand market, the traditional “kick the tyres” inspection has been replaced by a new technical gold standard: The Battery Health Certificate.
Understanding the State of Health (SOH) is no longer just for tech geeks—it is the single most important factor in protecting your car’s residual value.
What is a Battery Health Certificate?
A Battery Health Certificate is a verified diagnostic report that confirms the State of Health (SOH) of an EV’s high-voltage battery. Unlike the “State of Charge” (SOC), which tells you how much “fuel” is in the tank right now, the SOH tells you how much the “tank” has shrunk since the car left the factory.
- 100% SOH: The battery is performing at original factory capacity.
- 95% SOH: Typical for a well-maintained 3-year-old EV in the UK.
- Below 70-80%: The threshold where most manufacturer warranties (like Polestar’s 8-year/100,000-mile guarantee) may be triggered for a replacement.
Is it a Legal Requirement in the UK?
As of April 2026, there is no UK law making a battery certificate mandatory for private sales. However, the landscape is shifting rapidly:
- The “Battery Passport” Influence: The EU’s mandatory Digital Battery Passport (coming in 2027) has already set the standard. UK buyers are now demanding similar transparency, and many “Approved Used” schemes from brands like Volvo, Polestar, and Hyundai now include these certificates as standard.
- Consumer Rights Act 2015: For dealers, selling an EV with undisclosed, significant battery degradation can now be legally classified as “not as described” or “not of satisfactory quality,” leading to a surge in standardized testing.
How to Get a Certificate (and What to Look For)
If you are selling your EV on MotoringMojo, or looking to buy one, you have three main routes to certification:
1. Manufacturer Diagnostics
Visit a main dealer. They use proprietary software to check individual cell voltages and thermal history.
- Pros: Recognized by all buyers; usually free during a standard service.
- Cons: Can sometimes be “optimistic” as it’s calibrated by the people who provide the warranty.
2. Third-Party “Flash” Tests (e.g., Aviloo or Altelium)
These are independent tests where you plug a dongle into the OBDII port and drive the car from 100% to below 10%.
- Pros: Unbiased, incredibly detailed, and highly trusted in the private market.
- Cons: Costs between £60–£100.
3. The 2026 “Self-Check” Method
Most modern EVs (Tesla, Polestar, BMW) now have a “Battery Health” sub-menu in the infotainment system. While useful, a screenshot of this is often seen as “informal” compared to a third-party PDF certificate.
Checking Battery Health: The UK Top 5 (2026 Edition)
If you’re standing on a forecourt looking at a used EV, use these shortcuts to find the State of Health (SOH) before you sign the paperwork.
1. Tesla Model 3 / Model Y
Tesla remains the most transparent brand for battery data.
- The Shortcut: Tap Controls (Car Icon) > Service > Battery Health.
- The Pro Move: For a truly deep dive, press and hold the Model 3/Y Logo for 5 seconds, type the password
service, and enter Service Mode. This provides a granular view of cell voltages and total lifetime energy flow.
2. Polestar 2 (and Polestar 3/4)
Polestar’s Android Automotive OS updated in late 2025 to include a dedicated health suite.
- The Shortcut: Tap the Car Symbol on the bottom bar > Car Status > Battery.
- What to look for: It will display a “Battery State of Health” percentage and the “Distance driven since last estimation.”
3. MG4 EV
The UK’s favorite budget EV requires the MG iSmart app for the most accurate reading, though the dash provides basic alerts.
- The Shortcut: Open the MG iSmart App > Vehicle Status.
- The Deep Dive: Tap the “Health Scan” soft key. It will systematically scan the battery management system (BMS) and report if the status is “Normal” or “Abnormal.”
4. Volkswagen ID.3 / ID.4
VW’s “Software 4.0” and higher has made battery health more accessible.
- The Shortcut: Navigate to Vehicle > Charging > Battery Settings.
- The Pro Move: VW usually hides the exact SOH percentage from the main driver. To get a precise number without an OBD2 dongle, you can check the “Maximum Range at 100%” and compare it to the original WLTP figure (factoring in the 20″ wheels if applicable).
5. Kia Niro EV / EV6
Kia provides excellent energy usage data, but the SOH is best found via their connected services.
- The Shortcut: On the screen, press All Menus > EV > Energy Information.
- The Pro Move: Use the Kia Connect App. Under the “Status” tab, you can view the health of the “Battery Care” functions, which indicates if the pack is maintaining optimal thermal and voltage balance.
Summary Table for Buyers
| Car Model | In-Car Menu Location | Best Independent Tool |
| Tesla | Service Mode (service) | Tessie / ScanMyTesla |
| Polestar | Car Status > Battery | ABRP (with OBD2) |
| MG4 | iSmart App Health Scan | Car Scanner ELM |
| VW ID.3 | Vehicle > Charging | EVNotify |
| Kia Niro | EV > Energy Info | Soul EV Spy |
Mojo Tip: If you’re buying a used EV and the infotainment system doesn’t show a clear SOH percentage, ask the seller to charge it to 100%. If the “Projected Range” is more than 15% lower than the car’s original factory rating (accounting for weather), it’s time to request a formal diagnostic certificate.
The “Mileage Myth” of 2026
Recent data from the 2025/26 Battery Performance Index has debunked a major myth: High mileage does not equal a dead battery.
The study found that a 3-year-old EV with 80,000 miles (mostly motorway driving and home charging) often has a higher SOH than a 15,000-mile car that has been “deep cycled” (run to 0% and left in the heat) or exclusively rapid-charged at 150kW+ stations.
EV Battery Health: Frequently Asked Questions
1. How much battery degradation is “normal” in the UK?
According to the latest 2026 data from Geotab, the average modern EV battery degrades by approximately 2.3% per year. In the UK’s temperate climate, a well-maintained car should still retain over 80% of its original capacity after 8 years of typical driving.
2. Does rapid charging actually damage the battery?
Using a 150kW+ rapid charger isn’t “damage,” but it does accelerate wear. Frequent use of high-power DC charging (more than 12% of your total charging sessions) can double the annual degradation rate to about 3.0%. For maximum longevity, “low and slow” AC home charging should be your primary fuel source.
3. At what point is an EV battery considered “dead”?
In the used market, a battery is generally considered to have reached the end of its automotive life when its State of Health (SOH) drops below 70%. At this point, while the car is still drivable, the reduced range may no longer meet the needs of the average commuter. These batteries are often recycled for “second-life” home energy storage.
4. What does a standard UK EV battery warranty cover?
Most manufacturers in 2026 (including Polestar, Tesla, and VW) offer an 8-year or 100,000-mile warranty. This typically guarantees that the battery will not drop below 70% capacity. If it hits 69% within that window, you are usually entitled to a free repair or a refurbished replacement pack.
5. Can I improve my battery health after it has started to drop?
Battery degradation is a chemical process and is permanent; you cannot “fix” a degraded cell. However, you can slow down further loss by:
- Keeping the charge between 20% and 80% for daily use.
- Avoiding leaving the car at 0% or 100% for more than a few hours.
- Using pre-conditioning in winter to warm the battery before you drive or charge.
6. How much does a Battery Health Certificate cost in the UK?
A professional, independent SOH certificate (like those from Aviloo or Altelium) typically costs between £60 and £100. Many “Approved Used” dealers now provide these for free as part of their 2026 sales standards.
The Motoring Mojo Verdict
If you are buying a used EV in the UK this year, do not buy without a certificate. If the seller cannot provide a recent SOH report, factor the cost of an independent test into your offer. In a market where a replacement battery pack can cost upwards of £10,000, a £70 certificate is the cheapest insurance policy you’ll ever buy.
