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A battery readout is not a battery test
Two very different things get called an “EV battery check”. Here is how they differ, and why it matters when the battery is the value.
AVILOO battery testing, provided by Battery Health Check
When you buy or sell a used EV, the battery is most of the value, so how you check it matters. Two quite different things both get called a “battery test”. One reads a number the car already holds about itself. The other independently measures the battery and issues a certificate you can stand behind. This page explains the difference in plain terms.
The two approaches
A readout tool plugs into the car's diagnostic socket and reports the State of Health figure the vehicle's own battery management system (BMS) has already calculated. It is quick because it is not measuring anything, it is simply handing back a number the car holds about itself. There is no independent measurement, and there is no agreed industry standard for how accurate that self reported number is.
AVILOO measures the battery itself and calculates the current State of Health independently, rather than reading it back from the BMS. In AVILOO's own words, the figure a BMS reports “is based on manufacturer specific algorithms and can differ significantly from the actual state of the battery”. Independence is the whole point: it is what a buyer, a court, or a finance dispute will actually stand on.
Three reasons a readout cannot do what a test does
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It reads the battery's own homework, it does not measure the battery
Working out a battery's true usable capacity means watching how it behaves while it charges or discharges. A passive plug-in reader cannot do that. It can only return the number the car already calculated. An AVILOO test derives State of Health from the battery's measured electrical behaviour, drawing on the learnings of tens of thousands of full discharge tests, not from the car's own estimate.
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It cannot see inside the pack, to cell level
A single State of Health percentage is an average across hundreds of individual cells. A pack is only as strong as its weakest cell, so that average can look healthy while hiding one weak or out of balance cell, the kind of hidden fault that quietly costs real world range and speeds up further degradation. A readout that only reports the pack figure cannot reveal this. AVILOO analyses the battery down to individual cell level, showing the condition of each cell and flagging irregularities, and reports against the weakest cell rather than the average, which is where a hidden problem actually shows up.
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It cannot connect to the newest EVs at all
A basic readout only speaks the older CAN data language over the diagnostic port. The newest EVs increasingly put their deep battery diagnostics behind a high speed connection called DoIP (Diagnostics over Internet Protocol), which needs different wiring and a full network connection that a simple readout does not have. On those cars a readout cannot get a reading at all. AVILOO has been DoIP enabled since 2024, one of the first independent rapid EV battery tests in the world able to communicate this way, so it can test the newest models, including cars from Mercedes-Benz, Volvo, Polestar, Renault and Smart, where a readout draws a blank.
The difference in one real test
On a recent UK FLASH test, the car's own BMS reported 99% State of Health. The independent AVILOO measurement came out at 97.7%. Not a dramatic gap on that car, but it makes the point: the dashboard figure and an independently measured figure are not the same thing, and only one of them is independent evidence. On a tired battery the gap can be far wider, and a readout will never show it.
Side by side
| Feature | A battery readout | AVILOO independent diagnostics |
|---|---|---|
| Where the figure comes from | The car's own BMS, read over the diagnostic port | Independent measurement plus AVILOO algorithms |
| Independent of the car's own software | No | Yes |
| Works on the newest DoIP only EVs | No, cannot connect | Yes, DoIP enabled |
| Cell level detail | No, pack level average only | Yes, analysed down to individual cell |
| Reveals a hidden weak or imbalanced cell | No | Yes |
| Flags a replaced or non original battery | No | Yes |
| Independent certificate | A self generated report | TÜV Certified, sealed, QR verifiable |
| Battery warranty on the result | None | £2,700 AVILOO Battery Warranty, free to the buyer |
What an AVILOO test gives you
- An independently calculated State of Health, not the car's own BMS number.
- A TÜV Certified method (AVILOO is TÜV and CARA certified), independent of the manufacturer.
- Cell level analysis, the condition of each cell across the pack, not a single headline percentage.
- A 3 minute FLASH test on a stationary car through the OBD-2 port, with the certificate issued about three minutes after the box is connected, accurate to within about 3% of AVILOO's full PREMIUM discharge test.
- DoIP capability, so the newest EVs can be tested, not just older models.
- Over 95% EV and PHEV model coverage, with benchmarking against the same make, model, age and mileage.
- A certificate issued directly by AVILOO that no one, including us, can edit, with a QR code so a buyer can verify it is genuine.
More on the principle behind this: why an independent battery check matters.
The AVILOO Battery Warranty
Every qualifying FLASH test comes with the AVILOO Battery Warranty, £2,700, free to the end customer. It is insurance backed, VIN tied, transfers to a new owner, and runs for 12 months or 12,400 miles. It is AVILOO standing behind its own test, something a readout cannot offer.
Why this matters under the Consumer Rights Act 2015
For the first six months after a sale, the Consumer Rights Act 2015 places the burden of proof on the seller. An independently measured, timestamped certificate is exactly the kind of evidence that answers a battery complaint before it becomes a dispute. A readout, repeating the car's own figure, is not.
What to look for in any battery check
Whatever provider you use, a certificate worth relying on should be:
- Independent of the car's own BMS figure.
- Certified by a recognised body (AVILOO is TÜV Certified).
- Cell level, not a single headline number.
- Able to reach the newest EVs (DoIP capable).
- Verifiable by the buyer (for example, a QR code) and backed by a warranty on the result.
See a real battery certificate
Independent, TÜV Certified, and ready in about three minutes.
Battery Health Check is an independent provider of EV battery diagnostic services using AVILOO technology. This page has been prepared by Battery Health Check and is not an official AVILOO corporate publication.
We endeavour to provide accurate and up-to-date information, but details may change. If you spot an error, please let us know.