Key facts
- SOH calculations and reporting are not identical among vehicle manufacturers or independent tools.
- A reported percentage can use different capacity baselines, so comparisons need method details.
- A warranty capacity threshold is a contractual definition, not necessarily an instant battery-failure limit.
Quick answer: A battery state-of-health (SOH) reading describes a calculated battery condition under a particular method. A number such as 88% cannot be compared responsibly with another car’s 88% unless the original capacity baseline, diagnostic tool, battery pack and measurement context are understood.
Six questions that matter more than the headline percentage
- Who generated it? Was the figure issued by the vehicle, a manufacturer service tool or an independent third-party test?
- What is the baseline? Is it compared with factory usable capacity, nominal energy or another internally modelled reference?
- When was it measured? Is the report dated and linked to this vehicle’s VIN?
- How was it measured? Was it a simple diagnostic estimate, a controlled charge/discharge test, or an algorithmic assessment?
- What else was reported? Are there diagnostic faults, temperature anomalies or capacity imbalances that need professional review?
- Does it match the warranty? Are the warranty’s measurement method, exclusions and coverage dates documented?
Worked illustration: percentages and denominators
Consider two hypothetical packs. Pack A’s initial usable capacity is 60 kWh and its measured usable energy is 51 kWh: 51/60 = 85%. Pack B starts with 70 kWh and measures 59.5 kWh: 59.5/70 = 85%. They show the same illustrative SOH, but their current absolute energy is different. In practice the baseline and test method must also match; these simple divisions are not a manufacturer diagnostic algorithm.
SOH is not the dashboard range
The dashboard’s estimated range changes with driving style, temperature, recent energy use, tyre pressure and accessory loads. That dynamic estimate is not a direct, standardised laboratory SOH measurement. Our range-estimate explainer outlines the distinction.
What a buyer should ask the seller to provide
Request a VIN-linked, dated battery diagnostic report from an appropriate service provider, warranty documentation, repair/recall history, charging and ownership records where available, and a complete vehicle inspection. Also check whether the battery is owned, leased or subject to a subscription using our battery ownership guide.
Warning signs not answered by an SOH number
Unresolved safety recalls, isolation faults, damaged high-voltage components, abnormal warnings and visible accident damage require professional review independently of the SOH percentage. Never infer that a high SOH makes a damaged battery safe.
Frequently asked questions
Does 80% SOH mean the car drives exactly 80% of its original range?
No. Range is affected by many factors besides battery capacity, and SOH methods differ.
Does the manufacturer always accept an independent health report for warranty claims?
No. Warranty terms commonly specify approved conditions, measurements and claim procedures.
This guide explains interpretation, not diagnosis. Consult the manufacturer’s current documents and qualified inspection service.
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