Quick answer
Key takeaways
- SoH compares the battery’s usable capacity now with what it had when new.
- It’s a more stable number than the dashboard range estimate, and not the same as state of charge.
- Charging habits and climate matter more than mileage, so two identical cars can differ widely.
- Most manufacturers guarantee a minimum SoH, commonly around 70 to 75%, for about 8 years.
The simple definition
State of Health is a percentage that compares a battery's current usable capacity to the capacity it had when it left the factory. A battery at 100% SoH can store exactly as much energy as it could when new. A battery at 85% SoH can only store 85% of that original amount, which means less range between charges.
Think of it like a bucket that's slowly getting smaller with age. The bucket is still there and still works, it just doesn't hold quite as much as it used to. That's degradation, and it happens to every lithium-ion battery, EV or otherwise.
How SoH is actually measured
SoH is calculated by comparing the battery's current maximum usable capacity, measured in kilowatt-hours (kWh), against the manufacturer's original rated capacity for that model. A car that left the factory with 30kWh of usable capacity and can now only hold 25.5kWh is sitting at 85% SoH.
This is different from state of charge (SoC), which just tells you how full the battery is right now, and it's different from the range figure on the dashboard, which is an estimate affected by driving style, temperature and recent trips. SoH is the underlying, more stable number those other figures are built on top of.
What counts as good, average or poor SoH
There's no single pass/fail line, but as a general guide for a car used normally in a UK climate:
| Age | Typical SoH range | What it means |
|---|---|---|
| 1 to 2 years | 95 to 99% | Still essentially new |
| 3 to 4 years | 88 to 95% | Normal, healthy degradation |
| 5 to 6 years | 80 to 90% | Still very usable for most drivers |
| 7 to 8 years | 75 to 85% | Range reduction becomes noticeable |
| 9+ years | Below 80% | Worth closer inspection, especially on smaller-battery models |
These are broad benchmarks, not hard rules. A car driven gently, charged mostly on a home wallbox and kept out of extreme heat will often beat these figures. A car that's spent its life on rapid chargers in hot conditions may fall short. That's exactly why checking the actual figure matters more than guessing from age or mileage alone.
Why mileage isn't a good enough proxy
With a petrol or diesel car, mileage is a reasonable stand-in for wear and tear. With an EV, it's a much weaker signal. Two examples of the same model with identical mileage can have noticeably different SoH depending on how they were charged and where they've spent their life. A high-mileage motorway car charged carefully overnight can easily out-perform a low-mileage car that spent every summer parked in direct sun at 100% charge. This is the main reason a proper battery report matters more for EVs than a standard mileage check ever could.
How SoH connects to your warranty
Most manufacturers guarantee a minimum SoH for a set period, commonly somewhere in the 70 to 75% range over around 8 years, though the exact figure and the way it's measured varies by brand (some quote a plain percentage, others use a bar or segment display, like Nissan's 12-bar gauge, our Nissan Leaf battery health guide is a worked example). If a car is still within its original battery warranty and its SoH has dropped below the guaranteed threshold, that's genuinely useful to know before you buy, since a valid claim means the manufacturer repairs or replaces the pack for whoever owns the car when it happens. Our EV battery warranty guide covers what triggers a claim and how much cover transfers to you.
How to actually find out a car's SoH
The dashboard range estimate won't give you this, and some manufacturer apps only offer a rough approximation. A measured SoH percentage comes from a physical OBD test on the car itself, worth having at handover on a high-value EV. Before you view, the Used EV Check estimates the same picture from just the registration and mileage: the expected real-world range now versus when new, an estimated degradation figure for that specific vehicle, and a battery-health grade where a manufacturer test record exists, alongside the car's full MOT and mileage history. Range data is powered by ClearWatt.
For a step-by-step walkthrough, see our guide on how to check a used EV's battery health. And if you're still weighing up the bigger question, we cover the risks beyond the battery in is it safe to buy a used electric car?
Range and battery-health figures are estimates modelled from real-world data and are shown for the specific vehicle in the Used EV Check. Range data is powered by ClearWatt. A battery-health grade is shown where a manufacturer test record exists, it is a comparative grade, not a measured state-of-health percentage.
Want to know a specific car's estimated SoH?
Enter a registration to see a used EV's battery health, real-world range now vs when new and remaining battery warranty, an instant report for £9.99.
Frequently asked questions
Is a lower SoH dangerous?+
Can SoH improve over time?+
Does a low SoH mean I should walk away from a car?+
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