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EV battery state of health (SoH) explained

Published 2026-10-27 · Last updated 2026-10-27

State of health (SoH) is the single number most used to judge a used EV battery. This guide explains what it means, the different ways it is measured (the car's own reading, independent tests such as AVILOO, and range-based scores such as Recurrent's), why two readings of the same car can differ, what is typical at different mileages, and where battery warranties draw the line.

What SoH means

SoH is the energy the battery can hold now as a percentage of what it held when new. Certificates normally express it against usable capacity, the part of the battery the car lets you use (see our certificate guide). It is different from state of charge (SoC), the "battery %" on the dashboard, which tells you how full the battery is right now.

Illustration: an MG4 Long Range has a 64.0 kWh nominal battery with 61.7 kWh usable (EV Database). At 90% SoH it would hold roughly 0.9 × 61.7 ≈ 55.5 kWh, with range falling by about the same proportion in the same conditions.

Buffers: usable vs nominal capacity

EV batteries keep some capacity in reserve at the top and bottom of the charge window, so the dashboard's 100% and 0% are not the cells' physical limits. Recurrent says usable capacity is usually 95–99% of the total (Recurrent). The MG4 above has 64.0 kWh nominal and 61.7 kWh usable; the LFP Standard Range version has 51.0 kWh and 50.8 kWh (EV Database). Generational certificates print both figures (Generational).

Buffers explain why range can look stable as a battery ages: Recurrent says some makers likely release reserve capacity over time, while others (it names BMW and Jaguar) appear not to (Recurrent).

Three kinds of battery health figure

Some cars also run their own capacity test. Tesla's in-car Battery Health test runs the battery below 10% and recharges it on AC, taking up to 24 hours (Tesla UK).

Why two readings of the same car differ

• Different methods. On published AVILOO certificates that also print the car's BMS value, AVILOO's figure ranged from 2.2 points below to 2.9 points above the BMS figure (table below). In 2,742 AVILOO tests in Central Europe, the two readings were within 2 points for 62% of cars (Zuvala R., Bucsuhazy K., Kadula L., Dedek J., via Zenodo; our calculation from the published dataset).
• Tolerance. AVILOO states ±3% (AVILOO GmbH), and ADAC uses ±3 percentage points for its AVILOO-based long-term readings (ADAC). Treat 1–2 point differences as noise.
• Test conditions. DEKRA's driving test requires a state of charge of about 40–80% and a battery temperature of 10–30 °C (DEKRA).
• BMS recalibration. In a Technical University of Denmark study of one 62 kWh Nissan Leaf logged twice a day for 18 months, the SOH figure moved in steps roughly every 90 days, up as well as down, attributed to periodic updates of the car's capacity estimate (DTU – Technical University of Denmark). LeafSpy's documentation also notes that the meaning of its Hx value is "not fully understood" (LeafSpy).
• Software updates. One Kona Electric owner read 97.4% before a battery-management software update and 100.0% straight after, at about 52,000 km (single car, GoingElectric forum). Recurrent reports that software updates changed displayed range on some Ford and Hyundai models (Recurrent).

Single cars (n=1) – examples of the gap, not averages.

What's typical by mileage and age

By mileage (AVILOO tests, Central Europe, all models combined):

Source: Zuvala R., Bucsuhazy K., Kadula L., Dedek J., via Zenodo (2026-09-07); percentiles calculated by us from the published dataset.

By age (UK independent tests, BMS-based):

Source: Generational – UK, all models combined (BEV + PHEV, cars + vans), tested in 2025. Average SoH across all vehicles: 95.15%. In 4–5-year-old vehicles the lowest-performing 1% fell to 80.76%.

• Sweden, Sweden, all models combined, 9,954 AVILOO tests 2022–2026: 98.6% at up to 10,000 km, 94.4% at 50,000 km, 92.4% at 100,000 km (Carla AB).
• By model, the median at 100,000 km in AVILOO's 2026 report ranged from 88.3% (Nissan Leaf) to 95.3% (Hyundai IONIQ 5) across 20 models (AVILOO GmbH, 2026-09-03). See all models compared.
• UK auction cars: 1,000 Generational battery checks at Shoreham Vehicle Auctions (UK used EVs, all models): average SoH 98.7% under 4 years (656 cars), 92.6% at 4–6 years (279 cars, 83.5% above 90%), 88.8% at 6+ years (73 cars, 34.3% above 90%); overall median 95.6%, 88% above 90%, and only 0.4% below 80% (all older Nissan Leaf and NV200 Combi) (Motor Trader).
• Fleet data: Average degradation 2.3% per year across 21 make-models (2025 analysis of 22,700 fleet EVs); light cars averaged 2.0%/year, MPVs/light vans 2.7%/year; 8 of 11 established models from the 2023 dataset stabilised at 1.4%/year (Geotab). Ex-lease fleet, 24,000 certificates (Moba + AVILOO): about 93% average at 70,000 km; still above 90% at 160,000 km or 6 years; roughly 1 point lost per 25,000 km after a small early drop; newer generations 2–3 points higher (Arval).
• ADAC's rule of thumb for a used EV: at least 92% at 50,000 km, 88% at 100,000 km, 84% at 150,000 km, 80% at 200,000 km (ADAC).

Methods differ between these sources (AVILOO calculations vs BMS readings, medians vs averages, different countries and years), so compare a car with the source that used the same method where you can.

Warranty thresholds: when SoH becomes a claim

Of the 49 battery-warranty terms we track across 36 models, 36 pay out if capacity falls below 70% within the warranty period. The exceptions:

• Nissan Leaf – Pre-MY22 Leaf: below 9 of 12 capacity bars (5 years / 60,000 miles)
• Nissan Leaf – MY22-on Leaf: below 9 of 12 capacity bars (8 years / 100,000 miles)
• Škoda Enyaq iV – Bought with the UK electric car grant (from 2025): first 3 years: below 80% (3 years / 40,000 miles)
• Vauxhall/Opel Corsa-e (Corsa Electric) – "Electric All-In" offer cars: first 3 years: below 80% (3 years)
• BMW i3 – UK terms: "excessive loss of capacity" – % not stated on BMW's page (8 years / 100,000 miles)
• Renault Zoe – Battery owned, registered from 1 Mar 2020: below 80% (years 1–3), 70% (years 4–5), 66% (years 6–8) (8 years / 100,000 miles)
• Renault Zoe – Battery owned, registered before 1 Mar 2020: below 66% (8 years / 100,000 miles)
• Xpeng G6 / P7 – UK terms (G6 leaflet): not stated in the UK leaflet – ask XPENG (8 years / 100,000 miles)
• NIO ET5 – Germany: not stated in our source (8 years)
• Dacia Spring – UK terms: below 75% (8 years / 100,000 miles)
• Smart #1 – UK terms (version 21 Mar 2025): below 70% of the SoH at delivery (8 years / 125,000 miles)
• BMW i4 – UK terms: "excessive loss of capacity" – % not stated on BMW's page (8 years / 100,000 miles)
• Cupra Born – Bought with the UK Electric Car Grant (from 2025): first 3 years: below 80% (3 years / 40,000 miles)

Taken from each manufacturer's published terms (sources on each model page and in the warranty checker). Most terms also have mileage caps and conditions; always confirm the cover for the specific car with the manufacturer. Work out the time and mileage left with the battery warranty checker.

What SoH doesn't tell you

• It is a snapshot on the day of the test, not a forecast (AVILOO GmbH).
• It says nothing about cell balance or faults the car doesn't report; look at the cell voltage difference on the certificate (see the certificate guide).
• Range also depends on temperature, speed and driving style, so a range readout is not an SoH measurement (Recurrent).

Next steps: model pages with sourced data · battery health estimator · how to read a battery certificate · used-EV battery checklist and test prices · selling an EV: proving battery health.

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