- Gradual range loss is normal battery behaviour, not a defect. Sudden loss is a different problem and worth diagnosing.
- Manufacturers commonly cover the traction battery for about 8 years or 100,000 miles. That is prevailing practice, not one national rule. The booklet for your model year controls.
- Most battery warranties pay out on a capacity floor: coverage applies if capacity falls below a stated percentage, not simply because range decreased.
- State of health (SoH) is the number that matters on a used EV. Ask for a reading, not inferring from the range display.
- Heat, frequent DC fast charging and habitually sitting at very high or very low charge are the main accelerators of degradation.
Battery life questions usually mix three separate things: gradual capacity loss, outright failure, and what the warranty will actually pay for. They behave differently and are worth separating before shopping or worrying.
Gradual loss is expected chemistry. Outright failure is a fault. Warranty coverage is a contract with a defined period, a defined capacity threshold and defined exclusions. A vehicle can lose noticeable range and still be operating exactly as designed and entirely outside a warranty claim.
What degradation actually looks like
Lithium-ion capacity fades with time and use. The curve is not linear and the shape matters more than any single number.
Early loss, then a long plateau
Most packs show their steepest proportional loss in the first period of ownership, then settle into a much slower, roughly linear decline. An owner who sees a few percent early and extrapolates it across ten years will badly overestimate total loss.
Calendar ageing versus cycle ageing
Batteries age from sitting as well as from use. Calendar ageing is driven mainly by temperature and by the state of charge the pack rests at. Cycle ageing is driven by how much energy is moved through it.
This is why a low-mileage EV that spent years parked at full charge in a hot climate can show more loss than a higher-mileage car that was cycled moderately in a temperate one.
What accelerates it
Sustained high temperature is the single largest factor, which is why thermal management design matters. Frequent DC fast charging adds heat and stress. Habitually charging to 100% and leaving it there, or routinely running very low, both increase stress relative to cycling in a middle band.
- Heat: ambient and charging-induced
- Frequent DC fast charging, not slower AC charging
- Long periods resting at very high or very low state of charge
- Deep, repeated full-to-empty cycling
What the warranty actually covers
Coverage is specific, and the specifics are where expectations break. Manufacturers commonly cover the traction battery for about 8 years or 100,000 miles, and some states require longer terms for vehicles certified there. That length is prevailing manufacturer practice instead of a single national warranty rule, so the booklet for the exact model year is what controls.
Most battery warranties are written around a capacity floor. Coverage applies if measured capacity falls below a stated percentage of original within the covered period: commonly expressed as a retention threshold. Loss above that floor is considered normal and is not a claim, however disappointing the range display looks.
| Term | What to look for | Why it matters |
|---|---|---|
| Period | Years and miles, whichever comes first | Sets the outer boundary of any claim |
| Capacity floor | The retention percentage that triggers coverage | Determines whether gradual loss is claimable at all |
| Measurement | How capacity is assessed and by whom | Owner-visible range is not the diagnostic figure |
| Remedy | Repair, module replacement or full pack replacement | Module-level repair is common and is not a lesser outcome |
| Transferability | Whether coverage survives a sale | Decides how much value remains for a second owner |
| Exclusions | Collision, flood, unapproved repair, commercial use | The most common reason a claim is refused |
Two vehicles quoting the same years and miles can differ substantially in the retention percentage that actually triggers coverage. That percentage is the contract.
Buying a used EV: what to actually check
For a used EV the battery is the largest single component of value, and it can be assessed, not guessed. Treat it the way you would treat a used engine and transmission together.
- Get a state-of-health reading from the manufacturer's tooling or an approved diagnostic, not from the dashboard range estimate.
- Read the battery warranty for that exact model year, including the capacity floor and the transfer rules.
- Confirm how much of the period and mileage remains, and whether it transfers to you.
- Ask about charging history where it is available. A car fast-charged almost exclusively has had a harder life than one charged at home.
- Check for open recalls by VIN, since several battery-related campaigns have applied to specific build ranges.
- Note the climate the car lived in. Sustained heat is the most consistent accelerator of loss.
Why the range display is not state of health
The range number on the dash is a prediction based on recent driving efficiency, temperature and current charge. It moves with weather and driving style. State of health is a measurement of usable capacity against original capacity, and it is the figure a warranty claim would turn on.
Habits that measurably help
None of these are exotic, and most cost nothing.
Charge to a middle band for daily use
Many manufacturers provide a daily charge limit setting. Using it for routine driving, and charging to full only before a long trip, reduces the time the pack spends at high state of charge.
Prefer slower charging when time allows
AC charging overnight is gentler than repeated DC fast charging. Fast charging is a tool for travel, not a default.
Mind temperature when parking long-term
For extended storage, a moderate state of charge in a moderate temperature is better than full charge in heat. Follow the manufacturer's storage guidance for the specific model.
Precondition while plugged in
Heating or cooling the cabin while still connected uses grid energy instead of pack energy, which helps both range and, in cold weather, battery temperature.
Judging a used battery before you buy
The question is rarely 'will it fail': it is 'how much usable capacity remains, how much coverage remains, and what is that worth'.
- For a used EV: obtain a state-of-health reading and the remaining warranty terms before negotiating.
- Weigh remaining battery coverage the way you would weigh remaining powertrain coverage on any vehicle.
- For a new EV: compare capacity-floor percentages and transferability across the shortlist, not marketing lifespan claims.
- If range dropped suddenly instead of gradually, treat it as a fault to diagnose, not as ageing.
- Record the reading at purchase so future change is measurable, not remembered.
Slow decline within the stated floor is designed behaviour. A step change in range or available power is a diagnostic event and should be investigated under warranty while coverage remains.
Common questions
How long does an EV battery actually last?
Most packs outlast the warranty period, losing capacity gradually rather than failing outright. The practical question is how much usable capacity remains at a given age and mileage, which is measured as state of health instead of estimated from the range display.
Is the 8-year/100,000-mile battery warranty required by law?
That length is prevailing manufacturer practice, not a single national requirement. Some states impose longer terms for vehicles certified there. The warranty booklet for the exact model year is the controlling document.
Does battery degradation mean the car is broken?
No. Gradual capacity loss is expected lithium-ion behaviour and is normally excluded from warranty unless capacity falls below the stated retention floor. A sudden drop in range or power is different and should be diagnosed.
What is state of health and how do I get it?
State of health compares current usable capacity to original capacity. It is read with manufacturer or approved diagnostic tooling. It is not the same as the dashboard range estimate, which varies with weather and driving style.
Does fast charging damage the battery?
Frequent DC fast charging adds heat and stress relative to slower AC charging, and heavy reliance on it is associated with more degradation. Occasional fast charging for travel is what the system is designed for.
Should I charge to 100% every night?
For routine driving, many manufacturers recommend a lower daily limit and reserve full charges for long trips. Time spent resting at very high state of charge is one of the accelerators of calendar ageing.
Does the battery warranty transfer to a second owner?
Often yes, but the terms vary and some impose conditions. Because remaining coverage is a significant share of a used EV's value, confirm transferability in the booklet for that model year before purchase.
Can a degraded battery be repaired instead of replaced?
Frequently. Many packs are serviceable at module level, and a module-level repair is a normal remedy instead of a lesser one. The warranty text states which remedies the manufacturer may choose.