Selling an EV is not only about the battery's condition. It is about its history.

No. Access means very little here — five fixed rules apply:

• You sign in on Tesla's own site — we never see your password.
• Read-only access: we cannot control, unlock or start anything.
• We never wake your car.
• No location access — we do not even ask for it.
• You can revoke access at any time — with us or directly in your Tesla account.

No. We only request read permissions — we cannot control, unlock or start charging.

Tesla at launch: Model 3 and Model Y, Model S and Model X depending on the battery variant and model year. Two very different cell types were in circulation for the 2021 Model 3 base variant; we now read which one is fitted from the pack voltage, once a few data points above 65% state of charge are in. For Model S and Model X we issue for the 75 pack (2016–2019) and the Palladium generation (Plaid from 2021, Long Range from 2022); for the 60, 70, 85, 90 and 100 packs we lack a sourced reference value. Where it is missing, we say so instead of guessing. On the S and X the onboard computer matters too: cars built before March 2018 do not send their readings directly to us, and without that streaming no certificate can be issued. Connecting works for every Tesla. More brands will follow via official vehicle interfaces.

Connecting and building your Akkubrief are free. The signed Akkubrief is a one-time €79 at the moment of sale. We are currently in open beta: sales start after our validation study is published, planned for mid-January 2027. Your history is fully preserved until then, and early-access users get preferential terms.

Vehicle data is stored encrypted and never sold. Your connected vehicle always counts anonymously in our fleet analyses — only as a group value with a minimum group size, never with VIN, name or location; that is the deal behind building your Akkubrief for free. The signed Akkubrief shows the VIN only masked and as a checksum. Deletion at any time on request.

An independent project from Germany — not affiliated with Tesla. Our methodology and verification process are public.

You pay for the signed Akkubrief, not for a particular result. It documents the battery history it states and the current figure — whether that figure is high or low. It is only issued once the data supports it.

From what the car does while driving and charging: every unbroken movement of the state of charge is a measurement run, and its slope (energy per percentage point of charge) gives the capacity. Many runs combined with robust statistics yield a reliable range instead of a snapshot. The full methodology is publicly documented, including limits and a changelog.

How we calculate → methodology

Every connected vehicle adds to our data. That lets us study how batteries develop, and build comparison groups, across more and more vehicles. That is the deal, and we say it out loud.

In return, your connected vehicle always counts anonymously in our fleet analyses — only as a group value with a minimum group size, never with VIN, name or location.

You build your Akkubrief and watch its history — free.

We earn money at the moment of sale: when you issue your signed Akkubrief. It costs a one-time €79 at launch.

Beta here means one thing: you cannot buy an Akkubrief yet. Connecting and building run in full. The field study continues to issue signed certificates in the existing document version; individual Akkubrief documents can already be issued through unlock codes. Your figure is therefore not a preview: every Akkubrief states its range, and that range belongs to the method. We are still working on the method itself, at present mainly on the reference figure — the benchmark we hold your measurement against. What improves there is not the measurement of your car but the comparison. Public evidence across many vehicles is open as well. Our validation study freezes its dataset on 13 December 2026, publication is planned for mid-January 2027, and sales open after that.

What beta means → the full explanation