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. The good news: hardly any carmaker lets you inspect battery health in as many ways as Tesla. The bad news: 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 quietly 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 — no test cycle needed. Tessie costs roughly 7 to 13 US dollars 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, checkable 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 euros 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, accuracy around plus/minus three percentage points according to the provider. The shorter Flash test (about 3 minutes; 79 euros including certificate at ADAC Hessen-Thüringen) is aimed mainly at dealers and test stations.
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 — our approach
Full transparency: Akkubrief is our product. We connect through your Tesla account (read-only scopes, the car is never woken up), derive battery health from the charging history across many sessions instead of a single measurement, and issue a signed certificate any buyer can verify in the browser against the VIN — in minutes, without hardware, for a one-off 29 euros. Our methodology is published openly; the beta starts with a small group.
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 | SoH certificate (±3%) | yes |
| ADAC/Aviloo Flash | €79 | ~20 min on site | short certificate | yes |
| Akkubrief (beta) | €29 | minutes | signed certificate from charging history, verifiable online | yes |
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.