How to Check the State of Health of a Used EV Battery
Learn how to verify a used EV battery SOH claim by checking the metric, test method, date, scope, fault history and supporting report.
- Reviewed
- 27 August 2026
- Reading time
- 9 min read
- Written for
- commercial buyers, repairers and second-life battery project teams
Direct answer
Check what the SOH percentage measures, which new-battery reference it uses, how and when the test ran, whether it covers the whole pack, and which faults or exceptions appeared. Without those details, an SOH number is a seller claim, not verified battery condition.
Applies to: Commercial desk review of used EV packs and modules. This guide does not replace model-specific diagnostics, a competent high-voltage inspection or a buyer's technical acceptance procedure.
Example: A listing says a used EV battery has 90% state of health. That sounds precise. It still leaves the buyer with six unanswered questions: 90% of what, compared with which reference, measured how, tested when, covering which parts of the pack, and with which faults?
Do not dismiss the number. Use it as the start of the inspection. A traceable capacity test can support a buying decision. An undated dashboard screenshot cannot carry the same weight.
Start with six questions
| Check | Question for the seller | Why it changes the decision |
|---|---|---|
| Metric | Does SOH mean remaining energy, capacity, power, range or a BMS estimate? | Different metrics can produce different percentages for the same battery. |
| Reference | What value represents 100%? | Rated, certified and measured-as-new values are not interchangeable. |
| Method | Was this a controlled discharge, vehicle diagnostic, BMS reading or modelled estimate? | The method defines what the result can prove. |
| Date | When did the test run, and what happened afterwards? | Operation, storage and an incident after the test can change the pack. |
| Scope | Does the result cover the whole pack, selected modules or one vehicle-level estimate? | An average can hide a weak module or an unresolved pack fault. |
| Exceptions | What faults, imbalance, isolation issues or negative events were recorded? | A strong capacity result does not cancel a separate safety or reliability problem. |
If the seller cannot answer these questions, treat the percentage as unverified. Ask for the underlying report before pricing the pack as tested stock.
State of health is not one measurement
The EU Batteries Regulation separates several health and lifetime fields, including remaining capacity, power capability, internal resistance, round-trip efficiency, cycle count, temperature history and negative events. UN Global Technical Regulation No. 22 also distinguishes energy-based and range-based durability measures for vehicles.
These frameworks do not create one universal aftermarket grade for every used EV battery. They show why a single percentage needs a definition.
The EU framework applies directly in the EU and, under current UK government guidance, in Northern Ireland. It is not automatically the rule for a domestic sale in Great Britain. This guide uses its field structure because it makes a battery-health claim easier to inspect, including when no battery passport exists.
| Evidence | What it can tell you | What it cannot prove alone |
|---|---|---|
| Remaining capacity or energy | How much charge or usable energy the test recovered against a stated reference. | Power delivery, isolation integrity or future degradation. |
| Power capability | Whether the battery can deliver or accept power under stated conditions. | Total usable energy across the required operating window. |
| Internal resistance and module spread | Whether resistance or imbalance may limit performance or indicate inconsistency. | Root cause without further diagnosis. |
| BMS estimate | What the battery-management system currently calculates from its data and model. | Accuracy when the method, calibration and operating history are unknown. |
| Fault and event history | Whether recorded faults, over-temperature events or other exceptions need investigation. | Absence of every historical event when records are incomplete. |
What a useful SOH report contains
A buyer should be able to connect the result to the physical battery and reproduce the logic behind it.
Identity
- manufacturer, model and part number;
- pack or module serial evidence where appropriate;
- original vehicle or application;
- nominal energy, voltage and configuration;
- test subject: whole pack, modules or vehicle-level estimate.
Test record
- date and location;
- equipment, software and version;
- stated metric and 100% reference;
- starting and ending state of charge;
- temperature and rest conditions;
- load or test profile;
- measured result, not only the final percentage.
Exceptions
- diagnostic trouble codes;
- cell or module voltage spread;
- isolation or contactor findings where tested;
- temperature exceptions;
- known accident, water, fire or repair history;
- limits of the test and any part of the pack not assessed.
The report does not need to use one universal format. It does need enough detail for the buyer to understand what was measured and what remains unknown.
Worked example: two packs advertised at 90% SOH
The following example is illustrative. It shows how evidence changes a buying decision; it is not a market-price claim.
Pack A
The seller supplies the part number, serial evidence and removal history. A dated report defines SOH as remaining usable energy against a documented new-pack reference. It records the charge window, temperature, energy throughput, module spread, fault scan and test equipment. The pack remained in monitored storage after the test.
Buyer response: compare the result with the project's acceptance sheet. The buyer may make a conditional offer, subject to identity, physical inspection and any model-specific checks.
Pack B
The seller supplies a dashboard screenshot showing 90%. The image has no date. It does not define the metric, reference, software or part of the battery assessed. The seller cannot provide the fault report and describes the pack as “working when removed”.
Buyer response: request the missing evidence or price the pack as unverified. Do not treat the screenshot as equivalent to Pack A's report.
| Decision state | Minimum interpretation | Sensible next action |
|---|---|---|
| Evidence is traceable and matches the battery | The result can support a defined acceptance review. | Compare it with the use case and remaining commercial terms. |
| Evidence is partial but the gaps are clear | The result may support a conditional bid. | Request one targeted follow-up test or document. |
| The number has no method, date or scope | The condition claim is unverified. | Test, inspect or decline before paying a tested-pack price. |
When the recommendation changes
The required proof depends on what the buyer plans to do.
- Vehicle repair: exact compatibility, OEM procedures, pairing, faults and warranty boundaries may matter more than one capacity figure.
- Second-life storage: repeatable test data, power and energy requirements, thermal behaviour, pack consistency and future supply can dominate.
- Parts or module use: module-level measurements and safe, traceable disassembly matter. A pack-average result may be too broad.
- Recycling: SOH may have little bearing on treatment value, while chemistry, mass, condition, packaging and transport determine the practical route.
A healthy battery can still be the wrong battery. SOH evidence supports technical condition; it does not prove compatibility, authority to sell, safe transport or acceptable delivered economics.
A buyer's five-minute SOH screen
Before spending engineering time, ask the seller to complete this record:
| Field | Seller response |
|---|---|
| Battery identity and serial evidence | |
| SOH metric and 100% reference | |
| Test method and equipment | |
| Test date and conditions | |
| Whole-pack or module scope | |
| Measured result behind the percentage | |
| Faults, imbalance and exceptions | |
| Incident, repair and storage history | |
| Original report available? | Yes / No |
If the record is incomplete, the next step is clear: request the report, commission a competent test or stop the purchase. A vague number should create a question, not confidence.
Bottom line
The strongest SOH claim is not the highest percentage. It is the result with a clear metric, reference, method, date, scope and exception record. Ask for those details before you compare batteries or make an offer.
Review note: Recheck the EU and Northern Ireland battery-data position before 18 February 2027, and review the diagnostic examples whenever the cited standards or ReBattery evidence workflow changes.
Sources
- European Union, Regulation (EU) 2023/1542 concerning batteries and waste batteries, including state-of-health, expected-lifetime and battery-passport information fields.
- UNECE, UN Global Technical Regulation No. 22 on in-vehicle battery durability.
- European Union, Regulation (EU) 2024/1257 on Euro 7, including vehicle battery durability definitions.
- Office for Product Safety and Standards and Newcastle University, Safety of second-life batteries in battery energy storage systems.
- OPSS and Defra, EU Batteries Regulations in Northern Ireland.
- Health and Safety Executive, Electric and hybrid vehicles.