Short version: only a diagnostic read from the battery management system, confirmed under load, counts as a test. Everything else is an estimate — and estimates on a used EV have a habit of landing in the seller's favour. If you want the background on what the number means, start with the battery health check guide.
The four ways SoH gets measured
Ranked worst to best. Sellers quote the first two. Buyers should insist on the fourth.
Indicated range on the dashboard
A rolling prediction based on the last few hundred kilometres of driving, ambient temperature and climate use. A week of gentle commuting in mild weather can lift it noticeably. It tells you about the driver, not the pack. Useful only as a first smell test.
A consumer OBD app
A cheap dongle plus a phone app. On well-supported models it gets within a few per cent; on others it reads the wrong parameter entirely and reports nonsense with total confidence. It almost never shows cell voltage spread, which is where a failing module hides.
A full charge–discharge cycle
Genuinely accurate for total capacity — run the pack from full to nearly empty and measure the energy that came out. It also takes half a day, needs a charger, and puts a deep cycle through a battery you don't own yet. Nobody does this before a sale.
A diagnostic BMS read, confirmed under load
Manufacturer-level tooling reads the battery management system's own record of usable energy, every cell group's voltage, cycle counts and thermal history — then a road test and a live charge session confirm the pack behaves like the numbers say. This is what we do, and it takes about an hour.
What the read actually reports
The headline SoH percentage is one line of a battery report. These are the figures that change what a car is worth, and what you should offer for it.
| Reading | Healthy | Why it matters |
|---|---|---|
| Usable capacity | vs original spec | The real SoH percentage — kWh you can actually use today. |
| Cell voltage spread | Under ~30 mV at rest | A wide spread is the earliest sign of a module heading for failure. |
| Cycle count | In line with odometer | High cycles on low kilometres means short trips and constant topping up. |
| DC / AC charge mix | Mostly AC | An ex-rideshare car fast-charged daily has aged differently to its odometer. |
| Peak pack temperature | No sustained highs | Heat is the main driver of degradation in Queensland cars. |
| Isolation resistance | Within spec | A safety reading — moisture ingress or damaged insulation shows here first. |
| Stored fault history | Clear | Shows the faults that were reset before you arrived to look at the car. |
Every one of those readings is included in both of our inspection packages — the battery work is the part we never cut.
Where a number can mislead you
The buffered pack
Several brands hold a hidden reserve and spend it silently as the pack ages, so the displayed figure barely moves while usable capacity falls. The BMS knows. The screen doesn't say.
The recently reset BMS
Clear the modules and the pack reports optimistically until it has relearned over a few hundred kilometres. A suspiciously round, suspiciously high number on a car with recent "electrical work" is worth a second look.
The LFP exception
Lithium iron phosphate packs have a famously flat voltage curve, so estimation methods struggle with them. On an LFP car — most base-model Teslas and BYDs — an app estimate is close to worthless. Read more on how the two chemistries age.
Getting a test done in Brisbane, Sydney or Melbourne
We come to the car — a seller's driveway, a dealership forecourt, a workplace car park — anywhere from Brisbane, Sydney, Melbourne to the Gold Coast, Ipswich, Logan and the Redlands. The battery work takes about an hour, and it forms part of a full pre-purchase inspection rather than a standalone scan — a healthy pack in a car with a bent subframe is still a bad buy.
Ask for the car to be at roughly half charge and driven that day. A pack sitting on the charger at 100%, or one that's been parked for a fortnight, gives readings we have to caveat. If the result matters — and at these prices it does — the conditions matter too. Pricing is on the cost page.
Measured, not estimated.
A real state of health figure on the car you're about to buy, in writing, with the VIN on it.