Reading Tesla battery degradation without fooling yourself
"My range dropped 20 km — is the battery failing?" Nine times out of ten, no. You cannot judge degradation from one number; you need a line long enough to mean something.
Battery degradation is probably the thing Tesla owners worry about most, and also the thing they misjudge most. The question arrives weekly: my range is lower than when I collected the car — is it degrading badly?
Almost certainly not. The problem is the method.
Why a single reading tells you nothing
The estimated range on the screen is current charge multiplied by an estimated efficiency factor. That factor moves for reasons that have nothing to do with battery health:
- Temperature — usable capacity genuinely drops in the cold and comes back in spring;
- Recent driving — the estimate references recent consumption, so a few highway runs shift it;
- BMS calibration drift — if you only ever cycle between 20% and 80%, the battery management system lacks reference points and its estimate slowly loses accuracy;
- Software updates — the estimation algorithm changes and the number jumps with it.
So "10 km less than last week" carries essentially no information. The noise is far larger than the signal — what you are looking at is mostly the weather, not the battery.
The right way: a line long enough to read
What does mean something is the estimated capacity at each near-full charge, recorded over a year or two. The noise is still there, but the trend rises out of it.
MyTeslaCloud does this automatically — every charging session is captured and the battery trend chart connects the points. You do not have to record anything by hand. You only have to give it time.
| What to watch | Why |
|---|---|
| Full-charge capacity trend | The most reliable indicator; needs six months minimum to read |
| State of health (SOH) | A composite figure, useful for comparing against others |
| Charge-depth history | How high and how low you actually cycle — directly affects lifespan |
| Supercharger share | Heavy fast charging accelerates wear, though less dramatically than folklore suggests |
| Charging efficiency curve | Falling efficiency under similar conditions can be an early signal |
What normal degradation looks like
Published data and broad owner observation agree on the shape: degradation is faster early, then flattens. Losing a few percent over the first 10,000–20,000 km is common, after which the curve noticeably slows.
Put differently, a new car’s first year looks the most alarming and is usually exactly normal. What warrants attention is the curve steepening again after it has flattened — and to spot that, you need the flat section on record.
Which is why "start logging early" is not just a sales line. Without a baseline there is nothing to compare to; if you only start once you suspect a problem, the first half of the curve is gone for good.
Habits that actually matter
- Do not sit at 100% daily — prolonged storage at full charge is hard on lithium-ion. LFP packs are the exception: charging to full periodically is recommended so the BMS can calibrate;
- Do not linger at very low charge — worse than the occasional full charge;
- Prefer slow charging — mostly at home with Superchargers as backup beats the reverse;
- Precondition before fast charging in the cold — high power into a cold pack is harder on it;
- Leave it near 50% for long storage, neither full nor empty.
None of this is new advice. What is interesting is that once you log, you can see what you actually do — and charge-depth history frequently disagrees with how people remember their own habits.
Frequently asked questions
This is general guidance, not a diagnosis of any specific vehicle. If you suspect a fault, a Tesla service centre’s assessment is what counts.
