SoH is a comparison, not the charge level
State of charge describes how full a battery is now. State of health describes its condition relative to a reference, but the method and definition matter. A capacity-based SoH result and a power-performance assessment need not describe exactly the same thing. Before comparing percentages, identify what each report measures and which new-battery baseline it uses.
A percentage needs a denominator
For a simple capacity comparison, 54 kWh divided by a 60 kWh original usable baseline equals 90%. If someone instead divides by a 65 kWh gross rating, the apparent percentage changes even though the battery has not. This is why the original baseline, measurement boundary and units belong alongside the result. An unnamed percentage in an advert leaves too much unexplained.
Reported BMS SoH remains reported information
The battery-management system uses vehicle data and its own estimation method. EVVerity can display a number you supply, but cannot authenticate the report or verify which car it belongs to. We label it “Reported BMS SoH” and keep it separate from the capacity inferred from range and consumption. Agreement between methods is useful context, not proof that either is exact.
What to ask when someone quotes SoH
Ask for the test date, odometer reading, method, reference capacity and any supporting service notes. Check whether the installed battery has changed since the report. Avoid translating a single percentage into a precise remaining lifespan. Your practical question is whether the documented condition, usable range and charging behaviour meet your needs, with uncertainties made explicit.
Three numbers that answer three different questions
A seller might show all three of the following values on one screen. They cannot replace one another. Read the name and reference before using any number in a calculator.
| Number | Meaning | What it does not establish |
|---|---|---|
| 80% state of charge | The displayed charge level now | That 80% of original capacity remains. |
| 90% capacity-based SoH | A condition estimate against a defined reference | Exactly how far the car will drive today. |
| 54 kWh usable capacity | Energy available under the stated method | The original gross pack rating or fault-free operation. |
Why “90% health” still needs explanation
Consider a hypothetical report with 54 kWh current usable energy and a 60 kWh usable reference. Its simple capacity ratio is 90%. At 18 kWh/100 km that energy implies 300 km before a reserve; at 24 kWh/100 km it implies 225 km. The same capacity ratio supports different range outcomes. A report can also use a reference or internal BMS definition that differs from this simple ratio. Ask the provider to state the method rather than converting an unexplained percentage into kWh yourself. A high confidence label on EVVerity concerns the evidence you supplied, not independent authentication of the report.
Before you rely on the answer
- What exactly is the reference capacity?
- Is the percentage reported by a BMS or derived from an energy test?
- What conditions and limitations accompany it?
Worksheets and numerical scenarios are original EVVerity editorial examples. They are not observed vehicle results or market-price data.
Put the explanation to work
Use your own vehicle information, check the assumptions and see the calculation.
Battery Health Estimator →EVVerity estimates are informational and are not a substitute for a professional battery diagnostic or pre-purchase vehicle inspection.
Sources & editorial basis
- Tesla — battery health: an example of a manufacturer diagnostic
- US Department of Energy — EV batteries
Sources checked 23 September 2026. Practical checklists and worked examples are EVVerity editorial guidance. Read our methodology.