What state of health actually measures
State of health — SoH — is the usable capacity of the battery today expressed as a percentage of the capacity it had when it left the factory. A car delivered with 75 kWh usable that now holds 69 kWh is sitting at roughly 92% SoH. That's it. It is not a measure of how well the car drives, how healthy the charging system is, or how long the pack will last from here.
Two cars with identical SoH can still be worth very different money. One might have perfectly balanced cells and a clean thermal history; the other might be holding its average up while a single weak module drags on every charge. That's why we report cell voltage spread alongside the headline percentage.
Why the dashboard number lies
Almost every seller quotes range: "it still does 400 kilometres." Indicated range is a prediction based on recent driving, temperature and climate control use. Drive gently for a week in mild weather and the number climbs. It moves with the car's mood, not with the pack's capacity.
Some brands also hide degradation behind a buffer, so the displayed percentage stays flattering while usable capacity quietly falls. Reading the battery management system directly is the only way past that.
How a proper battery health check is done
Read usable capacity from the BMS
Not the dash. We connect to the vehicle and pull the battery management system's own record of usable energy, then compare it with the original specification for that exact variant.
Check cell voltage spread
A healthy pack's cells sit within a few millivolts of each other at rest. A wide spread means one group is aging faster than the rest, which is the early signature of a module failure.
Review charge and thermal history
Cycle counts, the DC-to-AC charging mix, and how often the pack has run hot. Two cars with the same odometer can have completely different histories — and completely different futures.
Test it under load
A road test plus a live charge session shows what the pack does when it's working: voltage sag under acceleration, taper behaviour on DC, and whether the cooling system keeps up. Static numbers alone miss all of that.
Cross-check warranty and recalls
Most battery warranties run to eight years and a capacity floor around 70%. Whether that cover transfers to you — and whether any battery-related recall is outstanding — changes the risk completely.
Each step is broken down in how a state of health test works. All five are part of our Complete inspection; steps one, two and five are included in Essential.
What's normal degradation?
Most mainstream EVs drop a few per cent in the first year or two, then settle into a slower, fairly linear decline. Use this as a sanity check, not a specification — chemistry, climate and use pattern all move the goalposts, and a Queensland car has had a hotter life than the same model in Melbourne.
| Age | Healthy | Worth investigating |
|---|---|---|
| 1–2 years | 95%+ | Below 92% |
| 3–4 years | 90%+ | Below 86% |
| 5–6 years | 86%+ | Below 82% |
| 7 years + | 80%+ | Below 75% |
Buying a Tesla specifically? See the Tesla battery health check. Full detail on the curve — by chemistry, kilometres and climate — is on what degradation is normal. Early air-cooled models are the exception: they degrade faster here, and we treat them differently. More on heat in the Brisbane and Gold Coast pages.
What you can check yourself
Do this
Charge to 100% and photograph the indicated range. Compare it to the original WLTP figure. Ask for charging app history. Look for a battery-related service or module replacement in the records.
Don't rely on this
Third-party phone apps that estimate SoH. They're a useful smell test, but they read a limited slice of data and can be several per cent out either way — in the seller's favour as often as yours.
The battery series
Four deeper answers on the pack.
Get the real number on the car you're buying.
Measured on site, anywhere in Brisbane, Sydney or Melbourne, with the result in writing inside 24 hours.