Tesla has built a battery health test into the car's own software. It runs from the vehicle's Service menu, needs the car plugged into a charger, takes the pack through a discharge and full recharge, and can take up to 24 hours. At the end it reports a capacity percentage. It is a genuine measurement — and it is the one test on this page that a used buyer cannot run, because it needs the car for a day.
What the in-app test does
It measures capacity by cycling the pack: running it down, charging it to full, and comparing what went in against what the pack held when new. That is closer to a laboratory method than to a diagnostic read, and Tesla uses it as the basis for warranty capacity claims. Owners should run it — it is free, and it is the most authoritative number a Tesla will give you.
Its limits are practical. It needs the car for up to a day, plugged in, and it needs the owner to start it. If you are buying a used Tesla from a stranger, you are unlikely to get either.
What a "degradation" number means
Teslas show range at 100% charge, and owners talk about degradation as the difference between that and the original rated figure. This is the least reliable version of the number: rated range changes with software updates, wheel choice and the car's own estimate of recent efficiency. A Model 3 showing 8% "degradation" on its range display may test at 4% capacity loss or at 11%.
The battery management system's own State of Health figure — which a diagnostic read reports — is closer to the truth than the range display, and the in-app cycle test is closer still.
What we can do at the car
An independent diagnostic read at the vehicle takes minutes, does not need the car plugged in for a day, and reports the pack's State of Health as the BMS tracks it, cell-group voltage spread, temperature behaviour and any stored or pending high-voltage fault codes. It is read-only, and a seller will allow it when they would never hand the car over for a 24-hour test.
Two Tesla-specific notes. Lithium-iron-phosphate Teslas — the rear-wheel-drive Model 3 and Model Y with the LFP pack — need a recent full charge for the BMS figure to be well calibrated, and Tesla itself recommends charging them to 100% regularly. A seller who says "I always charged to 100%" on an LFP Tesla was following the manual. On the nickel-chemistry long-range and performance cars, the same habit is a mark against.
The warranty numbers
Tesla guarantees 70% capacity for 8 years — 160,000 km on the standard-range rear-drive Model 3 and Model Y, 192,000 km on the long-range and performance cars — and the warranty transfers. Full terms: Tesla battery warranty in Australia.
What to check before you buy a used Tesla
Which pack — LFP or nickel — because it flips the charging advice
Measured State of Health from the BMS, not the range display
Cell voltage spread
Supercharging history, which the car records
Odometer against 160,000 or 192,000 km
Tesla Model 3 · Tesla Model Y · Book a test — $249
In-app test behaviour as described by Tesla in its owner documentation and software release notes. Warranty terms from Tesla Australia. Verified 15 September 2026.