What is a battery health report for an electric car?

When you're buying a used petrol car, you check the service history, the mileage, and the general condition. When you're buying a used electric car, there's one additional check that matters more than almost anything else: the battery health report. It tells you something a test drive can't — how much of the battery's original capacity is still there, and how much real-world range you can actually expect.

Battery degradation is gradual, invisible, and irreversible without a very expensive replacement. Understanding what a battery health report shows, how to read it, and what the figures mean in practice is one of the most useful things a used EV buyer can know. Here's a complete guide.

What is a battery health report?

A battery health report is a diagnostic read-out of an electric car's high-voltage battery pack. It summarises the battery's current condition compared to when it left the factory, typically expressed as a percentage of original capacity called State of Health (SoH).

A new EV battery starts at 100% SoH. Over time and use, chemical reactions inside the battery cells cause gradual, irreversible capacity loss. This is normal — all batteries degrade — but the rate varies significantly depending on how the car has been used, how it's been charged, and the chemistry of the specific battery pack.

A battery health report translates the diagnostic data from the battery management system (BMS) — the computer that monitors and controls the battery pack — into a readable summary of current health, usually including the SoH percentage, the usable energy capacity in kWh, and sometimes the estimated real-world range at full charge.

Why does it matter more than mileage?

Mileage is a reasonable proxy for wear on a petrol or diesel engine, but it's a much weaker predictor of battery condition. Two EVs with identical mileage can have very different battery health depending on their charging history.

A car with 40,000 miles that was regularly charged to 100% using rapid DC chargers in hot weather will typically have degraded more than a car with the same mileage that was charged to 80% overnight on a slow home charger. The charging pattern, thermal management quality, and the frequency of deep discharges all affect the battery significantly more than raw mileage alone.

This is why a battery health report is essential rather than optional on any used EV purchase. Mileage without battery data tells you only part of the story.

What does State of Health (SoH) actually mean?

State of Health is the core metric in any battery health report. It compares the battery's current maximum capacity to its original rated capacity and expresses the result as a percentage.

A battery with 90% SoH retains 90% of its original range. On a car originally rated at 250 miles of real-world range, 90% SoH means a maximum of around 225 miles from a full charge — in typical conditions. A battery at 80% SoH on the same car would deliver around 200 miles.

The relationship isn't always exactly linear because other factors affect real-world range — temperature, speed, heating and cooling use, driving style — but SoH gives you a reliable baseline for comparison.

What SoH percentage is healthy for a used EV?

There's no single answer, because it depends on the age and mileage of the car and the expectations of the buyer. But the following is a practical framework used across the industry:

Above 90% SoH is excellent for a used EV of any age. The battery has degraded minimally and real-world range will be very close to what the car delivered when new. This is the target for buyers who want near-new performance from a used car.

85–90% SoH is good and typical for a well-maintained used EV in the 2–4 year old bracket. Range reduction is modest — around 10–15% less than when new — and for most drivers with realistic daily ranges, this remains entirely practical.

80–85% SoH is acceptable but worth factoring into your assessment. On a car with a larger battery pack (60kWh or more), this still leaves plenty of usable range for most drivers. On a smaller-pack city EV, the effective range reduction becomes more noticeable.

Below 80% SoH warrants careful thought. Most manufacturers set their battery warranty threshold at 70–75% SoH — meaning the battery is guaranteed not to fall below that level within the warranty period. A car reading below 80% is approaching that threshold faster than average and may indicate a heavier charging history or a less well-managed battery. It doesn't make the car a bad buy, but the asking price should reflect the reduced battery performance.

What else appears in a battery health report?

Beyond the headline SoH figure, a thorough battery health report typically includes additional data that helps paint a fuller picture:

Remaining usable capacity (kWh). The actual energy the battery can store and deliver at the point of testing, expressed in kilowatt-hours. This is the most direct measure of what you're getting, independent of the car's original rated capacity.

Full charge range estimate. Many reports include an estimated real-world range from a full charge based on current battery capacity. This is more useful than SoH percentage alone for buyers who want to understand day-to-day practicality.

Number of charge cycles. Some reports include the cumulative number of full charge cycles the battery has completed. This gives context to the SoH figure — a high SoH with a very high cycle count is more unusual and worth noting. Battery manufacturers typically rate their packs for several hundred to over a thousand full cycles before significant degradation is expected.

Cell balance data. More detailed reports include data on the voltage balance across individual battery cells or cell groups. A well-balanced battery — where all cells are performing consistently — indicates a healthy pack. Significant imbalance between cells can be an early indicator of developing problems and is worth flagging to a specialist.

Maximum charge rate. Some systems report the battery's current maximum charging rate, which can decline slightly with age. This affects how quickly the car charges on a rapid charger.

How is a battery health report produced?

Battery health reports are generated by connecting a diagnostic tool to the car's OBD-II port or a manufacturer-specific interface and reading data from the battery management system. The method varies by brand:

Tesla makes battery data accessible directly through the car's own touchscreen display. Under Settings — Software, the energy app and range display give a real-time view of the battery's current maximum range. Third-party tools such as Scan My Tesla provide more detailed cell-level data. Tesla's battery is also monitored through the car's connected services.

Kia and Hyundai EVs can be assessed using official dealer diagnostic tools (GDS for Kia, GDS Mobile for Hyundai) which produce a detailed SoH report including cell balance data. Third-party tools such as EVSpy Pro and OBDLink also access much of this data on these platforms.

Nissan Leaf uses a proprietary system. Nissan dealers can produce a battery health report, and the leaf-specific tool LEAF Spy (used with a compatible OBD adapter) has become the standard independent diagnostic tool for Leaf batteries, providing detailed cell data and an accurate capacity reading.

BMW and Mini EVs can be assessed through the BMW dealer network using their ISTA diagnostic system, which produces comprehensive battery health data.

Most other modern EVs can be assessed using either manufacturer dealer tools or established third-party platforms. The quality and detail of the data varies by brand and model year.

Does Carsa offer battery health reports?

Yes. At Carsa, battery health reports are available on request for any used electric car in our stock. If you're considering a specific EV and want to see the current SoH and capacity data before making a decision, ask our team and we'll arrange the report for you.

We believe buying a used electric car should come with the same transparency and confidence as buying any other used car at Carsa — and a battery health report is a straightforward way to give buyers the information they need. All our used cars are comprehensively inspected before sale and come with a 90-day warranty as standard.

What should I do if the SoH figure is low?

A lower SoH figure doesn't automatically mean a car isn't worth buying — but it should be reflected in the asking price and it changes the conversation around practical range.

If you're shown a battery health report with an SoH below 80%, the first step is to calculate the realistic range you'd actually have. Take the car's official WLTP range, multiply by the SoH percentage, and then apply a further 10–15% reduction for the gap between official and real-world figures. That gives you a conservative estimate of the range you should plan around.

If the figure is below 75% and the car is still within the manufacturer's battery warranty period, it's worth contacting the manufacturer or a franchised dealer — because most battery warranties guarantee at least 70% SoH for eight years or 100,000 miles, and a car reading below that threshold may be eligible for a warranty replacement.

For cars outside the warranty period, a lower SoH should simply be reflected in a lower asking price. The car still works — it just has less range than when it was new — and the reduced price should compensate for that accordingly.

How to get the best from your EV battery going forward

If you're buying a used EV with a healthy battery, protecting that health going forward is straightforward. The habits that preserve battery capacity are well established:

Charge to 80% for everyday use and reserve 100% charges for longer journeys. Most EV manufacturers and battery experts recommend keeping the daily charge level between 20% and 80% to reduce stress on the cells. The last 20% of charging — from 80% to 100% — is the most chemically demanding for the battery.

Avoid regularly running the battery down to 0%. Deep discharges accelerate degradation. Keeping the battery between 20% and 80% in everyday use is the single most effective long-term preservation habit.

Use rapid DC charging thoughtfully. Fast charging is not inherently damaging in moderation, but regular reliance on ultra-rapid charging (150kW+) as the primary charging method can accelerate degradation over time. Home overnight charging on an AC wallbox is the gentlest and most battery-friendly option.

Park and charge in moderate temperatures where possible. Extremes of heat and cold both stress the battery. Most modern EVs have active thermal management to mitigate this, but parking in shade in summer and a garage in winter reduces the thermal workload on the battery management system.

Find a used electric car at Carsa

Carsa stocks a wide range of used electric cars, all priced on average £700 below market value and comprehensively inspected before sale. Battery health reports are available on request for any EV in our stock — just ask our team. Every car comes with a 90-day warranty as standard, and finance is available from 8.9% APR (10.9% APR representative).

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