How to Read a Battery Health Report
Battery State of Health is the single most important number when buying a used EV. Here's exactly what it means, how it's measured, and what to look for.
What is State of Health (SoH)?
State of Health (SoH) is a percentage that shows how much of an EV battery's original capacity remains. A brand new battery is 100% SoH. Over time, through charging cycles and temperature exposure, the battery degrades slightly.
Think of it like this: if a Nissan Leaf had 168 miles of range when new (100% SoH), and now shows 85% SoH, its maximum range is now around 143 miles. The car still works perfectly — it just has slightly less range than when it was new.
Quick SoH reference guide:
How is SoH measured?
SoH is measured using specialist diagnostic software connected to the car's OBD-II port (the same socket a mechanic uses for diagnostics). The software reads data directly from the Battery Management System (BMS) — the car's computer that monitors battery health.
Different cars store this information differently:
Nissan Leaf
The Leaf has a built-in battery health display accessible through the car's own menu system. It shows a capacity bar (up to 12 bars) which gives a rough SoH estimate. Specialist tools like Leaf Spy give precise percentage readings.
Tesla
Tesla displays battery health as "rated range" in the car's settings. The original rated range vs current rated range gives you an approximate SoH. Tesla's own service app can provide a more detailed report.
Hyundai, Kia, Volkswagen, others
These require specialist OBD tools (such as OBDII readers with appropriate software) or dealer diagnostics to read accurate SoH data. An EV-specialist mechanic can provide this report for £50–£100.
What causes battery degradation?
All EV batteries degrade over time — it's normal and expected. The rate of degradation depends on several factors:
Age
Medium impactAll batteries age naturally. A 5-year-old EV will have some degradation regardless of mileage.
Mileage
Medium impactEach charge cycle contributes to degradation. High mileage generally means more cycles.
Rapid charging frequency
High impactFrequently using 50kW+ rapid chargers causes more degradation than home charging. Check if the seller used rapid chargers heavily.
Heat exposure
High impactBatteries degrade faster in hot climates. Less of a concern in NI's mild climate.
Charging habits
Medium impactKeeping the battery between 20–80% extends life. Regularly charging to 100% or letting it drop to 0% accelerates degradation.
Battery chemistry
High impactEarly Nissan Leafs (2011–2015) used less advanced chemistry and degrade faster than modern EVs.
How to get a battery health report before buying
Ask the seller directly
Any reputable dealer should be able to provide a battery health report. If they can't or won't, that's a red flag. All EVHubNI dealer listings include SoH data where available.
Get an independent EV inspection
For private sales especially, consider paying for an independent EV health check from a specialist. These typically cost £100–£150 and include battery health, charging system check, and a general inspection. Several NI garages now offer this service.
Check the car yourself (for Nissan Leaf)
If you're buying a Nissan Leaf, you can check the battery bars yourself during the test drive. Navigate to the vehicle information menu and look for the battery health indicator. 12 bars = full health.
Use an OBD reader app
A cheap Bluetooth OBD reader (£20–£30) combined with the right app can read SoH from many EVs. Apps like Leaf Spy (Nissan Leaf), ScanMyTesla (Tesla), and Car Scanner work well. Ask the seller if you can plug one in during the test drive.
Battery warranties — your safety net
Most EV manufacturers offer a separate battery warranty alongside the standard vehicle warranty. These typically guarantee the battery won't fall below a certain SoH threshold (usually 70%) within a set period.
| Manufacturer | Battery Warranty | SoH Guarantee |
|---|---|---|
| Nissan (Leaf) | 8 years / 100,000 miles | 75% |
| Tesla | 8 years / 100,000–150,000 miles | 70% |
| Hyundai (Kona) | 8 years / 100,000 miles | 70% |
| Kia (e-Niro) | 7 years / 100,000 miles | 70% |
| Volkswagen (ID range) | 8 years / 100,000 miles | 70% |
| MG | 7 years / 80,000 miles | 70% |
| Renault (Zoe) | 8 years / 100,000 miles | 66% |
Warranties listed are for new vehicles. Used EVs may have remaining warranty — check with the seller or manufacturer.
How EVHubNI shows battery health
Every listing on EVHubNI shows the battery SoH as a percentage badge on the listing card and as a detailed bar on the listing page. Listings with verified battery health reports from specialist assessors are highlighted with a verified badge.
We also show estimated winter range based on SoH and known model data — so you can see exactly what real-world range you'd get in a Northern Ireland January, not just the optimistic official figures.
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Every EVHubNI listing shows SoH data, real-world range, and winter range estimates. Buy with confidence, not anxiety.
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