The shape of the curve
Battery degradation isn't a straight line. Most packs drop two to four per cent in the first year or two as the cells settle, then flatten into a slow, fairly linear decline of roughly one to two per cent a year. That initial step alarms new owners and means almost nothing.
The curve turns again much later, when individual cell groups start falling out of step with the rest. That's the phase you're trying to detect on a used car — and it shows up in cell voltage spread long before it shows up in the headline percentage.
Normal by age and odometer
Age and kilometres age a pack by different mechanisms — calendar ageing and cycle ageing — so both matter. Read the two columns together: a low-kilometre car that's been sitting in the sun at 100% for five years can be worse than a high-kilometre garaged one.
| Age | Odometer | Expected SoH | Walk-away line |
|---|---|---|---|
| 1–2 yrs | Under 40,000 km | 95–98% | Below 92% |
| 3–4 yrs | 40–80,000 km | 90–94% | Below 86% |
| 5–6 yrs | 80–130,000 km | 86–91% | Below 82% |
| 7–8 yrs | 130–180,000 km | 80–88% | Below 75% |
| 9 yrs + | 180,000 km + | 72–84% | Below 70% |
Treat this as a sanity check, not a specification. It's built from what we measure on South East Queensland cars — a Melbourne or Hobart example of the same model will usually read a point or two better. Below the walk-away line, the question stops being "how much do I offer" and becomes "what's wrong with it" — see how SoH is tested.
Chemistry changes the answer
NMC / NCA
The long-range chemistry — more energy per kilo, more sensitive to heat and to sitting at high charge. Follows the table above. Owners are told to keep it around 80% day to day, and the ones who didn't show it.
LFP
Standard-range Teslas, most BYDs, some MGs. Tolerates daily 100% charging, handles heat better and typically ages slower — but its flat voltage curve defeats app-based estimates, so it needs a proper read to assess at all.
Air-cooled early packs
Pre-2018 Nissan Leaf and a few contemporaries have no liquid cooling. In this climate they can be ten to fifteen points below the table at the same age. Priced accordingly, they can still be a fine city car — just never assume the table applies.
What accelerates it here
Heat and time at high state of charge do most of the damage, and South East Queensland supplies plenty of both. A pack that spends summer sitting at 100% on a driveway in Ipswich has a harder life than one that commutes daily between 30% and 70%.
Parked outdoors at high charge
The worst combination there is: a hot pack held near full. Garaged cars in the same suburb read measurably better.
Near-exclusive DC fast charging
Occasional fast charging is fine. Daily fast charging on an ex-rideshare or ex-delivery car is a different pack to the same model that lived on a home charger.
Long storage near empty
Cars left on a dealer's back lot for months at a low charge can wake up with a flat 12-volt battery and a pack that has quietly drifted out of balance.
Towing and heavy loads
Sustained high current plus heat. Not disqualifying, but a tow bar on a five-year-old EV is a reason to read the thermal history carefully.
Wear, or a fault?
This is the distinction that decides whether you negotiate or walk. Normal degradation is gradual, even across the pack, and roughly matches age and use. A fault looks different: a step change in capacity, a cell group sitting well below its neighbours, a car that's lost fifteen points in three years, or stored codes for isolation and thermal events.
It matters commercially, too — a genuine fault inside the coverage period is usually a manufacturer's problem rather than yours, which changes the whole negotiation. Check the terms before you buy on the battery warranty page, and see what a pack costs if it isn't covered.
Find out where this car sits on the curve.
We measure it on site anywhere in Brisbane, Sydney and Melbourne, Monday to Friday.