Checking Tesla Battery Health: Every Method Compared (2026)
The traction battery is the most expensive single component of your Tesla and question number one when buying or selling a used one. Tesla lets you inspect it in an unusual number of ways — which is also the problem: the methods differ enormously in effort, meaning, and in whether the result proves anything to a buyer.
Option 1: The built-in battery health test
Since software version 2025.8.3 the test lives in the car under Controls → Service → Battery Health. It measures energy retention versus new in percent and recalibrates the BMS along the way.
The hurdles are real: state of charge must be at or below 20 percent to start, the car needs AC charging at roughly 5 kW or more (wall connector, no Supercharging), the test runs up to 16–18 hours depending on the source, and it is limited to one run per six months. Also important: with update 2025.26 Tesla removed the test, or reduced it to read-only, on many vehicles. Whether your car still offers it, only the car itself will tell you.
Strength: free, a real measurement, recalibrates the BMS. Weakness: slow, not universally available. And it remains the manufacturer's self-assessment: shareable as a screenshot, verifiable by no one.
Option 2: Service mode (the predecessor)
The same measuring approach has existed longer in service mode: car plugged in, discharge to a low state of charge, full charge to 100 percent, result shown as "Battery Health" in percent. Typical duration 12 to 24 hours, considerably longer on weak AC. Workable for a technically minded seller, impractical for a buyer at a viewing.
Option 3: App self-diagnosis and displayed range
In the Tesla app, Service → Battery and Charging → Range leads to a quick self-diagnosis: it tells you whether your car is "within normal degradation" — nothing more, no percentage. And the displayed range at 100 percent? A BMS estimate that drifts without regular calibration. Both are early-warning tools, not a basis for a deal.
Option 4: Owner apps (Tessie, TezLab)
Apps like Tessie continuously read vehicle data through the Tesla API and estimate battery health after every substantial charge, without any test cycle. Tessie costs roughly $7 to $13 per month depending on the tier, with detailed battery tracking in the Pro plan. For owners who want to watch their pack over the years, this is a fine route. For selling, the catch remains: the number lives in your app — it never becomes a neutral, verifiable document for the buyer.
Option 5: Hardware tests (Aviloo, ADAC)
Austrian provider Aviloo is the established name for independent battery testing. The Premium test costs €99 in Germany: connect the box (on a Tesla via the included adapter cable), drive the pack from 100 percent to below 10 percent (you get up to seven days for that), and receive a certificate with an SoH figure. The shorter Flash test (about 3 minutes; €79 including certificate at ADAC Hessen-Thüringen) is aimed mainly at dealers and test stations; it reads the vehicle's signals and calculates the SoH from them with a fleet model rather than passing on the battery computer's figure. Aviloo states the same accuracy for both tests: a deviation of at most ±3% in at least 95% of reference measurements (the provider's own figure, as of 2 September 2026).
Strength: independent, established, accepted by marketplaces like mobile.de. Weakness: hardware logistics and effort. And every measurement remains a snapshot of one single day.
Option 6: Akkubrief — a battery history rather than a measurement
Full transparency: Akkubrief is our product. It appears in this list but belongs in a different column from the five options above it. Those all measure today's condition. Akkubrief records it over time and turns that into a battery history.
In practice: we connect through your Tesla account (read-only scopes, the car is never woken up), determine the same quantity again and again across many charging sessions, and issue a signed document any buyer can verify in the browser against the VIN — without hardware, for a one-off €79 (incl. VAT). You can buy it once the results of the validation study are published; connecting and building the history cost nothing and are open now. Our methodology is published openly.
The price is not the difference that matters here. Every other option on this page is still available to you the day before a viewing. A history is not: it has to have started earlier. If a sale is still being planned, that choice is open; if the listing is already up, one of the tests above is the sensible route.
Head-to-head
| Method | Cost | Duration | Result | Provable to a buyer? |
|---|---|---|---|---|
| In-car test | €0 | up to ~16–18 h | percentage, BMS recalibration | no (self-assessment) |
| Service mode | €0 | 12–24 h+ | percentage | no |
| App self-diagnosis | €0 | minutes | only "normal / abnormal" | no |
| Tessie and friends | ~$7–13/month | continuous | trend + estimate | no |
| Aviloo Premium | €99 | up to 7 days of driving | certificate from the discharge record (±3% per the provider) | yes |
| ADAC/Aviloo Flash | €79 | ~20 min on site | certificate with SoH and benchmark (±3% per the provider) | yes |
| Akkubrief | €79 incl. VAT | builds from the moment you connect | signed document from the battery history | yes |
On the price in the last row: you can buy the Akkubrief once the results of the validation study are published. Connecting and building the history cost nothing and are open now.
Our take
For your own curiosity, the in-car test or the app will do. If you are selling, you need two things: a robust figure and a document the buyer can trust. That is where the roads part: a hardware snapshot, or history-based data via API. We believe in the latter; our reasons are laid out openly in our methodology.