EV battery health: separate capacity, charge and displayed range
Three different readings
DOE provides background on EV batteries. For a particular car, distinguish state of charge, battery health and displayed driving range. A partly charged battery is not necessarily degraded, and a change in estimated range is not by itself a capacity test. Vehicle settings, temperature and recent driving conditions must be recorded before comparing readings.
A record for a specific vehicle
| Item | Record or request |
|---|---|
| Identity | Model year, battery variant, mileage and service history |
| Warranty | Original terms, dates, mileage limits and transfer rules |
| Condition | Relevant faults, repairs and manufacturer inspection findings |
| Measurement | Test method, usable capacity boundary and conditions |
| Range | Charge level, weather, route and auxiliary loads |
| Charging | Manufacturer instructions for the exact model |
Ask what a seller’s health percentage means and how it was obtained. A dashboard estimate, an app’s calculation and a manufacturer diagnostic report can have different methods. Mark unavailable evidence as unavailable.
What a capacity ratio actually says
Suppose a fictional diagnostic method reports 54 kWh of usable energy against a comparable 60 kWh reference. The ratio is 90%. It is meaningful only if the test and reference share the same usable-energy definition and conditions. It does not independently determine road range, future ageing or a warranty remedy. This example is not a test we performed.
Use instructions for the actual car
Follow the manufacturer’s charging and storage guidance for the model. Generic rules can overlook chemistry, software and thermal management. For a purchase, obtain relevant inspection and warranty confirmation rather than extrapolating a fleet average to one vehicle. A clear unknown in the record is preferable to a promised remaining battery life without evidence.
Sources and scope
- US DOE Alternative Fuels Data Center: electric vehicle batteries — General battery context; exact warranty and operating instructions are manufacturer-specific.
Sources checked October 10, 2026. AI-assisted research and drafting. The examples, calculations and worksheets are Luminesca editorial work; they are not measured trials, first-hand reporting or an independent certification. Removed a fleet-average loss rate presented as a prediction for every vehicle. Report a specific correction with its source.