The battery warranty: what it promises and what it does not

Two entirely different claims get mixed up in everyday speech. One is the statutory guarantee of conformity: it runs against the seller and applies where the car did not have the agreed qualities at handover. The other is the manufacturer's warranty: a voluntary promise that sits alongside the statutory right and whose content the manufacturer defines itself.

In the European Union the statutory guarantee runs for a minimum period set by the sale of goods directive, which individual member states extend; for used cars a shorter period can in some cases be agreed. Switzerland has its own rules. Which period applies where you live and for which kind of seller is a question for the relevant consumer protection body — and only for them.

In practice the manufacturer's warranty is almost always the relevant promise for the battery, because it runs longer and because it explicitly covers the case a battery actually presents: not failure, but fading.

A battery warranty consists of three figures, all set out in the warranty terms: a period, a mileage — whichever comes first — and a capacity threshold. The promise reads, in substance: if usable capacity falls below this threshold within that period, the defect will be remedied.

Two things about that are regularly misread. First, the threshold is not a target but a floor: a battery just above it is as promised, even if the owner is unhappy with the range. Second, the warranty is not a promise of a new pack — it promises restoration to the agreed threshold, not to as-new condition.

Which threshold, which period and which mileage apply is stated only in that manufacturer's terms for that model year. They differ, they change, and second-hand information is worthless in a dispute. Ask for the document, not for the statement.

A battery has no odometer. Its remaining capacity is estimated by the battery management from voltages, charge counts and models — and that estimate drifts depending on how the car was last used. A car moved only between forty and sixty per cent for a long time gives a less accurate figure than one recently charged full and run well down.

So the warranty terms usually prescribe a procedure: measurement at an authorised workshop with the manufacturer's diagnostic tool, sometimes after a specified preparation such as a full charge and a settling period. A reading from a third-party app is a good indication when buying but is not proof against the manufacturer.

If it comes to a claim: the measured value carries a tolerance. Just above the threshold, a second measurement after a full charge and a longer drive is worth having before the claim is refused. Just below it, the workshop will want to document it — and that documentation is what counts.

The warranty covers capacity falling below the threshold and the failure of components inside the pack. It does not cover normal ageing above the threshold — that is expressly anticipated — and it does not cover damage from outside. The usual exclusions are much the same in nearly every set of terms:

The most important exclusion is not in the list at all but follows from how the promise is built: dissatisfaction with the range gives no claim as long as capacity stays above the threshold. Being unhappy is not a defect.

Almost every manufacturer's warranty attaches conditions the owner must meet. The commonest is keeping to the prescribed service intervals at an approved workshop. On an electric car that looks absurd, because there is barely anything to service — the inspection mainly checks brake fluid, the coolant circuit, software and the state of the high-voltage connections. It gets skipped all the same, and then the record is missing.

The second duty concerns software. Part of battery ageing is managed through the charging strategy, and manufacturers ship updates for it. Skip them and you risk the objection, in a claim, that the car was not operated in its intended state.

The third concerns charging habits, and here the terms are usually softer: recommendations on state of charge during long periods of standing, notes on how often to fast charge. They are rarely drafted as hard obligations but serve the manufacturer as an argument in a dispute. Anyone who charges gently anyway has nothing to worry about.

If a claim is accepted, a new pack does not automatically follow. The terms normally give the manufacturer the choice, and the most economical solution is usually replacing individual modules or a factory repair. The result is a pack back above the promised threshold — not one with as-new capacity.

Technically that is defensible as long as the modules fitted match the rest. Mix modules of markedly different age and the weakest one dictates the behaviour of the whole pack, because cells in series see the same current and the management has to work to the weakest link. A good workshop selects modules with matching remaining capacity; it is rarely documented.

It is still worth asking: has any work been done on the pack, and if so what exactly? A repaired pack is not a blemish, but it belongs in the history — and at the next measurement it explains why one module voltage sits out of line.

Manufacturer warranties on the high-voltage pack normally pass to the next owner; the warranty follows the car, not the person. On a used purchase that is worth real money and is one of the few points that can be quantified exactly: months left and kilometres left to the limit.

Two conditions often attach. The first is notifying the change of keeper, sometimes within a deadline. The second is territorial scope: warranties apply to a defined sales region, and a car imported from another region does not automatically fall under it. On an imported car that is the first question, not the last.

A franchised dealer can check it from the chassis number. The answer is free, takes minutes, and is the difference between a car with warranty left and one without — on two otherwise identical listings.

Five documents are enough, and all five are obtainable. A missing one is no reason to walk away, but it belongs in the price:

That takes barely an hour, split between a call to a franchised dealer and a question to the seller. Measured against the share of the purchase price the battery represents, it is the cheapest part of the inspection.

The order decides. First the measurement at an authorised workshop, documented in writing with date, mileage and the capacity measured. Then the claim to the manufacturer, or through the workshop, also in writing. Verbal assurances at the counter cannot be found again later.

If the claim is refused, ask for the reasons in writing with reference to the specific clause. That is not confrontation, it is the precondition for checking the objection. Many refusals rest on a missing record that can be supplied.

If the answer stays no, most countries have arbitration bodies for disputes between consumers and vehicle manufacturers, alongside general consumer arbitration. Which one has jurisdiction is a question for the consumer protection organisation where you live. That route is usually cheaper than litigation and starts with exactly the documents listed above.