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Knowledge base · 11 May 2026

EV battery state of health: the test every used buyer needs

State of health is the single number that decides whether a used EV is worth its asking price. Here's what it means, how to get it measured, and what's normal at one, three, and five years old.

State of health (SOH) is the percentage of original capacity an EV battery still holds. A new car is 100%. A perfectly normal three-year-old EV is somewhere between 94 and 97%. A car at 85% has lost a noticeable amount of range and probably has a deeper underlying issue.

You can drive an EV happily without ever knowing the number. You should not buy one without it.

What "state of health" actually measures

The chemistry inside an EV battery degrades with time, with cycle count, and with how the car has been treated (fast charging frequency, exposure to extreme temperatures, sitting at 100% charge for weeks). The result is that the usable capacity shrinks over years.

State of health is the simplest summary of that degradation:

SOH = current usable capacity / original usable capacity × 100

A 77 kWh battery (original usable) at 95% SOH is operating as a 73 kWh battery. Range drops proportionally: a car that did 250 miles real-world new will do roughly 237 miles at 95%, and 200 miles at 80%.

Most modern UK-market EVs report SOH internally. Some do not display it to the driver, which is why a battery health test from a dealer or independent specialist matters: they read it directly from the car's CAN bus using a diagnostic tool.

What's normal at each age

These are typical figures for UK-market BEVs from 2020 onwards. Anything older has more variability; anything wildly outside these bands warrants questions.

AgeMileageTypical SOHConcern threshold
1 year10 - 15k97 - 99%< 95%
2 years20 - 30k95 - 98%< 92%
3 years30 - 45k93 - 96%< 90%
5 years50 - 70k90 - 94%< 86%
7 years70 - 100k86 - 92%< 82%

These bands hold for healthy cars across the major UK platforms (E-GMP for Hyundai / Kia, MEB for VW Group, Tesla Model 3/Y after the early 2018 cohort, BMW i-series after iX1 generation). Older Nissan Leafs and some early Renault Zoes degrade faster.

How to get it tested

There are three sources, ranked by how trustworthy each is.

1. Dealer SOH report (most authoritative)

Main-dealer EV service centres can produce an SOH printout from the car's diagnostic system in 15 to 30 minutes. Many will do it free as part of pre-purchase inspection if you're buying from them, or for £30 to £80 if you bring an externally-sourced car.

Skoda, VW, Audi, Hyundai, Kia, Tesla and BMW main dealers all support this in 2026. Lookup is by VIN.

2. Independent EV specialist

Recurrent Auto, Cleevely Motors, EV Specialists, and a growing list of regional independents run SOH tests using OBDII diagnostic tools. £40 to £100 typically. Often more useful than a dealer because they'll tell you why the number is what it is — fast-charge history, extreme-temperature exposure, whether the battery has been replaced.

3. Aftermarket OBD reader app

OBDLink MX+ adapter plus the EV Toolbox or similar app reads SOH from the car directly. £70 for the adapter, £15 for the app. Works on most VW Group, Hyundai/Kia, and Tesla EVs. Less reliable on BMW and very new models.

Useful if you're privately inspecting a friend's car before buying. Less useful in a forecourt where the dealer doesn't want you plugging things into their stock.

When to walk away

  • Anything below 90% on a 3-year-old car. That's faster than typical degradation and usually has a root cause (heavy DC fast charging, frequent 100% charging, climate exposure, or an underlying cell-balance issue).
  • A car the dealer won't or can't produce an SOH report for. In 2026, that's a flag. Either they don't have access to the diagnostic, or they don't want to share the number. Either way, it's not your problem to solve.
  • A "we don't have those figures" answer. If the dealer is selling a used EV, they should know SOH. If they don't, get it tested independently before signing.

When to negotiate, not walk

A car slightly below the typical band — say 92% at three years — isn't necessarily a problem, but it's leverage. Equivalent cars in the same age band are at 95%; you can reasonably argue the price needs to reflect the gap. 3% of capacity is worth roughly 3% of the car's price to the next buyer in three years' time, so the discount should be in that range.

The warranty backstop

Most UK-market EVs carry a battery warranty of 7 to 8 years and an SOH floor:

  • Most major manufacturers warranty that the battery will retain at least 70% of original capacity within 8 years or 100,000 miles, whichever is sooner.
  • Kia goes further: 70% at 7 years / 100k miles.
  • Tesla on the Model 3 and Model Y: 70% at 8 years / 100k - 120k miles depending on variant.

This is not a guarantee that you'll never lose range. It's a floor below which the manufacturer is on the hook to repair or replace. In practice, claims at 70% are rare; most batteries hold 80% or above well past warranty expiry.

The trip-planning consequence

State of health feeds directly into how far an EV will actually go. A 5-year-old car at 90% SOH gives you 10% less range than the brochure suggests, plus all the usual real-world losses (temperature, speed, heater).

The real-world range calculator lets you plug in SOH alongside the other factors to see what a specific car will actually do in your conditions.

What this means for the buyer report

Every Compass EV buyer report includes a buying-checklist section flagging "get an SOH report" as item one. We don't have access to the specific cars in your shortlist until you're standing next to them at the dealer, so we can't pre-check it for you. What we can do is tell you what number to expect for the age and mileage of the cars we've recommended, and the threshold below which to negotiate or walk.