EV state of health

EV state of health is the dated assessment of the remaining capacity and performance of an individual EV battery, relative to a stated reference, based on battery management system data and, where applied, direct tests. State of health supports decisions about repair, resale, second life, and recycling, and the passport record should show the measurement, the method, the reference, and the date for each assessment. Article 14 and Annex VII address access to battery management system data for the purpose of assessing state of health and expected lifetime, for the battery owner and for persons acting on behalf of the owner, among others. A state of health figure without a method and a date cannot support a sale or a second life decision, because the buyer cannot know what was measured.

State of health means the assessed condition of an individual battery, commonly expressed as a percentage of a reference capacity, under stated conditions. The scope is individual EV batteries in use, at assessment, and at transfer.

How is the EV category decided?

EV state of health applies to that category, and the record should state the vehicle category, the weight basis, and the reason the battery falls inside the definition. Article 14 is the operative provision for the point in question, and Annex XIII sets the passport content where a passport applies. A diagnostic technician assessing state of health for a used EV battery should not assume that a traction battery for another vehicle type follows the same entry. A used EV pack offered for sale should show a state of health assessment with the method, the reference capacity, the date, and the data source, so a buyer can compare it with another pack assessed under the same method.

How are model and individual layers kept separate?

For EV state of health, the record should keep the two layers separate, with a link from the individual record to the model record. Battery management system extracts, test results, and assessment notes for a model value should name the test or calculation method and the date, while evidence for an individual value should name the measurement, the date, and the source system, such as the battery management system. State of health estimates from different methods, such as capacity tests, resistance measurements, and model based estimates, can differ for the same battery, and the record should state the method for each figure rather than average figures from different methods.

How are performance values stated?

For EV state of health, a capacity value, a power value, a cycle life value, or a capacity retention value should state the test conditions, the reference temperature, the charge and discharge rates, and the end point used. A diagnostic technician assessing state of health for a used EV battery should record which requirement applies to the EV battery in question and which requirement does not, with the article reference. A used EV pack offered for sale should show a state of health assessment with the method, the reference capacity, the date, and the data source, so a buyer can compare it with another pack assessed under the same method.

How is use phase information recorded?

For EV state of health, state of health, cycle count, temperature history, and fault history, where recorded, should be tied to the unique identifier and dated, so a later reader can see the sequence. Battery management system extracts, test results, and assessment notes should include the data extraction date and the version of the software or method used, where that information is available. State of health estimates from different methods, such as capacity tests, resistance measurements, and model based estimates, can differ for the same battery, and the record should state the method for each figure rather than average figures from different methods.

How are repair and second life operations distinguished?

For EV state of health, the record should name the operation, the operator who carried it out, the date, the parts changed, and the tests applied after the operation. A diagnostic technician assessing state of health for a used EV battery should check whether a new passport, a linked passport, or an updated passport is required for the operation, and should record the reasoning. A used EV pack offered for sale should show a state of health assessment with the method, the reference capacity, the date, and the data source, so a buyer can compare it with another pack assessed under the same method.

How is access and handover handled?

For EV state of health, the passport access rules in Article 77 set different levels for the public, for persons with a legitimate interest, and for authorities and notified bodies, and the record should not promise wider access than the Regulation allows. State of health estimates from different methods, such as capacity tests, resistance measurements, and model based estimates, can differ for the same battery, and the record should state the method for each figure rather than average figures from different methods. A diagnostic technician assessing state of health for a used EV battery should retain the handover record with the identifier, so a later dispute can be traced to a dated transfer.

How is a state of health figure audited for one battery?

Auditing one figure starts with the battery identifier, the assessment date, and the data source. The auditor reads the battery management system extract, checks the cycle count and the capacity estimate, and compares the estimate with a direct test where one was done. A worked audit shows the extract date, the method, the reference capacity, the result, and the auditor. If the extract and the direct test differ by more than the stated tolerance, the audit records the difference and the decision: accept the direct test, repeat the assessment, or mark the figure as uncertain. A figure that cannot be traced to an extract or a test is an unaudited figure, and the sale or transfer record should say so.

A state of health figure is useful only with its method and date, and a figure that hides its method asks the next holder to trust a number without a basis.