The battery is the most expensive component in an electric car, and state of health (SoH) is the number that prices it. More useful than the odometer, it decides how far the car really drives on a charge, what the car is worth, and how often you will be standing at a charger. Here is what battery health means for range and for money, the maths behind both, and how to test it before you buy in Australia.
- 2.3%
- average yearly battery capacity loss across 22,700 EVs analysed by Geotab
- 96%
- average state of health across 1,500+ EVs tested by Pickles in Australia
- ~6%
- average price uplift for EVs sold with a battery health certificate
What battery health actually means
State of health is the battery's current usable capacity as a percentage of its original capacity. A car that left the factory with 60 kWh of usable battery and now tests at 90% health has 54 kWh to work with — and unlike a fuel gauge, what is lost does not refill. Degradation is gradual rather than a cliff: large fleet datasets put the average around 2.3% a year, with charging habits and climate moving a car well above or below that line.
Battery health is how much energy the pack can hold compared with when it was new. Battery charge is how full it is right now. A full battery at 90% health still holds less energy than a full battery at 100% health — and every range estimate on the dashboard is calculated from what the car believes both numbers to be.
How battery health affects driving range
Range is energy divided by consumption: usable kWh ÷ kWh per 100 km × 100. Because health shrinks the usable energy, it shrinks range by the same proportion — a battery at 90% health delivers about 90% of its original range, all else equal.
A worked example, for a car with 60 kWh of original usable capacity, 90% health and 16 kWh/100 km consumption:
| Result | Calculation | Estimate |
|---|---|---|
| Remaining usable energy | 60 kWh × 90% | 54 kWh |
| Full-charge equivalent range | 54 ÷ 16 × 100 | 338 km |
| Range between 80% and 20% charge | 54 × 60% ÷ 16 × 100 | 203 km |
The third row is the one that matters day to day. Most owners charge to around 80% and avoid running below 20%, so the usable window is roughly 60% of the pack — at 90% health, about 203 km, not the 338 km the brochure figure suggests.
In everyday terms: at 50 km of driving a day, that window covers about four days between charges. At 85% health it is closer to three and a half. That translation — from a percentage to how often will I actually charge — is what most buyers are really looking for, and it is exactly what MotorLoop's EV calculator does: it opens from an electric listing with the car's battery details and consumption prefilled, and turns your daily driving into an estimated range, days between charges, a weekly charging cost and a home charging time. Where a car has verified battery evidence the calculator uses it; where it has none, the health figure is labelled as an assumption rather than presented as a fact about that car.
Health is not the only variable, and it is not even the biggest one on any given day. Tesla's own range guidance distinguishes the battery's energy retention from the factors that decide range on a particular drive: temperature, speed, terrain, climate control, load and tyre choice. Two identical cars at identical health can return very different numbers across a Melbourne winter and a Brisbane summer.
What battery health means for the price
Replacement packs run into the tens of thousands of dollars on many models, which is why what a battery replacement really costs sits behind every used-EV valuation. State of health is the closest thing a used EV has to an odometer for that component.
The market already pays for evidence. Pickles — which has battery-tested more than 1,500 EVs and found an average state of health of 96%, with cars beyond 120,000 km still around 90% — reports that EVs sold with a battery health certificate achieved an average price uplift of about 6%, with more bidders and more bids per vehicle.
Two practical rules follow:
- Price on evidence, not on age. Degradation is gradual and strongly shaped by charging habits and climate, so two cars of the same year and kilometres can be meaningfully different batteries. The full degradation data is in how long an EV battery really lasts.
- Be wary of precise formulas. There is no defensible "dollars off per health point" rule yet — the transaction evidence is still emerging. A verified low result is still verified: an honest 85% car priced accordingly can be a better buy than an unsupported 95% claim, because you know exactly what you are paying for.
If you are selling, the same logic runs in reverse: a current independent certificate is one of the cheapest ways to defend your asking price.
Does a degraded battery cost more to run?
Mostly no — and this is widely misunderstood.
Degradation reduces how much energy the battery holds; it does not materially change how efficiently the car uses that energy. A car at 90% health does not use 10% more electricity per 100 km — it simply needs charging about 10% more often.
What you pay per 100 km is consumption adjusted for charging losses. Home AC charging is typically around 90% efficient, so at 16 kWh/100 km and a $0.30/kWh tariff: 16 ÷ 0.90 × $0.30 ≈ $5.33 per 100 km — a figure set by your tariff and the car's efficiency, not by its battery health. The full breakdown is in what an electric car actually costs to run, and the running costs calculator does the maths with your own numbers.
The indirect cost of lower health is time and convenience rather than kilowatts: more frequent charging sessions, and more of them on expensive public fast chargers if your daily range becomes marginal.
How to test battery health
From cheapest to most rigorous:
- The car's own display. Some models show a capacity or health estimate. Treat it as a rough guide: the figure comes from the manufacturer's own algorithm and can read high or low against the pack's real condition.
- An OBD2 dongle and a model-specific app — Leaf Spy for the Nissan Leaf, Scan My Tesla, OBD Fusion for the Ioniq 5/6 and EV6, CanZE for the Zoe. These read cell-level data the dashboard hides; a wide spread between cell voltages is a warning sign whatever the headline number says.
- An independent battery health certificate. RedBook Inspect offers an AVILOO battery test with its mobile pre-purchase inspection (inspections from $295, the battery test as an add-on) in NSW, Victoria, Queensland and WA; Manheim issues AVILOO certificates at its Melbourne, Sydney and Brisbane auctions; the NRMA offers member-discounted battery health checks in Sydney metro and Canberra; mycar offers a report under the name Voltest; and mobile operators such as TESTMYEV come to the car — confirm coverage, supported models and how the report is validated before booking.
One distinction worth knowing: AVILOO itself separates its diagnostic products, and a quick screening score is not the same measurement as a capacity-based state-of-health certificate. Ask which test a report represents before relying on the number.
Whatever the source, judge the evidence, not just the figure.
A battery report only means something if it answers five questions: who tested the car, with what method, on what date, at what odometer — and whether the report is matched to that car's VIN. A certificate for a different car, or a dashboard screenshot with no date, tells you nothing.
How to verify a used EV's battery before you buy
Ask for the evidence
Request the battery report or certificate and check the provider, test method, date and odometer at testing — and that the VIN matches the car in front of you.
Read the car's own estimate
Note the dashboard or energy-screen figure as a rough guide, knowing it comes from the manufacturer's algorithm and can read high or low.
Get an independent measurement
For any car you are serious about, commission an OBD read or a professional certificate — an AVILOO test through RedBook Inspect or Manheim, or an NRMA, Voltest or mobile equivalent.
Do the range maths for your driving
Multiply the original usable capacity by the tested health for remaining kWh, divide by the car's consumption, then apply your real charge window — 80% down to 20% for most drivers.
Compare the price against known-health cars
Pay for verified evidence rather than age or claims — and negotiate from the certificate, not from the dashboard.
Reading a result: above 90% is excellent, 80–90% is normal at three to five years, below 75% is significant, and a large spread between cells is a red flag at any headline number. Treat those as rules of thumb rather than standards. Everything beyond the battery is in buying a used electric car: the checklist.
Keeping a battery healthy
Charging habits matter more than age. In Geotab's dataset, cars charged mostly at low power degraded about 1.5% a year, while cars frequently using DC fast charging above 100 kW degraded about 3.0% a year — and hot climates added roughly 0.4% a year, which is directly relevant here. Home charging at low power, with fast charging kept for trips, is the biggest lever an owner controls. The how-to is in charging an electric car at home and EV charging speeds explained, and the full degradation evidence is in how long an EV battery really lasts.
Related reading
- How long an EV battery really lasts
What large real-world datasets show about EV battery degradation, how often batteries are actually replaced, what the warranties guarantee, and how to check state of health before you buy a used one.
- Buying a used electric car: the checklist
What to check on a used EV that does not apply to a petrol car — battery state of health, charging history, which cables should come with it, connector type, warranty servicing conditions and recalls.
- EV battery life, warranties and what a replacement really costs
How long EV batteries actually last in Australia, what the standard 8-year warranty covers (and the degradation clause most people miss), real replacement cost ranges, and how to read battery health before buying used.
FAQs
What is a good battery health percentage for a used EV?
Above 90% is excellent, 80–90% is normal for a three-to-five-year-old car, and below 75% is significant enough to price carefully. Most used EVs test better than buyers expect: Australian testing of more than 1,500 EVs by Pickles found an average state of health of 96%, with cars beyond 120,000 km still around 90%.
Does 90% battery health mean 10% less range?
Yes, in round terms. Range scales with usable capacity, so a pack at 90% health delivers roughly 90% of its original range, all else equal. Conditions still move the real figure — temperature, speed, terrain, climate control and load matter on every drive.
Does a worn battery cost more to charge?
Not meaningfully per kilometre. Degradation reduces how much energy the battery holds, not how efficiently the car uses it, so you charge more often rather than paying more per 100 km. Your cost per 100 km is set by the car's consumption, your tariff and charging efficiency — around 90% for home AC charging.
Can I test EV battery health myself?
You can get a solid indication with an OBD2 dongle and a model-specific app — Leaf Spy, Scan My Tesla, OBD Fusion or CanZE — which reads cell-level data the dashboard hides. For a purchase decision, an independent certificate (AVILOO via RedBook Inspect or Manheim, an NRMA check, Voltest or a mobile provider) carries more weight with sellers, lenders and insurers.
Is the battery figure a seller quotes reliable?
Treat an unverified figure as a claim, not a measurement. Ask who tested the car, with what method, when, at what odometer, and whether the report is matched to the car's VIN. A current independent certificate answers all five; a dashboard screenshot answers none of them.
How long do EV batteries last?
Much longer than the myths suggest. Large datasets put average degradation around 2.3% a year and battery replacements under 4% outside recalls — with modern EVs far lower again. The full evidence is in how long an EV battery really lasts.