Replacing the battery: what makes it expensive

On a combustion car the risk is spread over many components: gearbox, turbocharger, particulate filter, timing chain. Any of them can be expensive, none is existential. On an electric car one single component is so expensive that its failure decides whether the car is a write-off — and that same component is the one that visibly ages.

Statistically, failure is rare. The great majority of traction batteries outlast the car without ever being replaced; the commonest repair on a high-voltage system is not to the cells but to the peripherals. The question is still legitimate, because an individual case is not an average.

What you will not find here is a figure. Pack prices differ by multiples depending on capacity, design and country, and they have been falling for years. What remains is the structure: knowing which items make up a quote lets you compare two of them and see where one is too high.

A quote for replacing a pack consists of four blocks, and only one of them scales with capacity.

So a quote without itemised lines says little. Ask for the split between parts and labour — only then can you tell whether a second quote is cheaper because it uses cheaper parts or because it books fewer hours.

A traction battery is not a block but an arrangement of modules, themselves made of cells. If one cell fails, technically only one module is affected. Whether that can be swapped alone depends on the design: bolted modules in an accessible casing can be changed for a reasonable outlay; bonded cells or cells integrated into the structure cannot.

The trend is towards packs in which the cells are part of the car's structure. That saves weight and space and is an advantage in use — in a repair it is the reason only the whole pack can be replaced. Buying an older car with bolted modules buys a repair option that newer cars no longer offer.

In a module swap, selection is everything. Cells in series see the same current; the management has to work to the weakest link. A new module beside heavily aged ones therefore delivers less than expected, and a badly mismatched one can keep the balancing busy indefinitely. A careful workshop measures the existing modules and picks one that matches.

A battery whose capacity has faded over the years is not broken. It is doing what lithium-ion cells do: with every cycle the passivation layer on the anode grows a little, binding lithium that is then no longer available for storage. On top of that comes calendar ageing, which runs without use at all and depends on temperature and state of charge.

That is why the curve is not linear: capacity falls more sharply in the first year, flattens afterwards and steepens again at the very end of life. A car still clearly above eighty per cent after several years has been treated well — one with the same mileage and notably less has not.

In practice: fading capacity almost never leads to a replacement, only to shorter legs. Replacement becomes an issue when there is a genuine fault, or when what is left no longer suits the use — and the latter is a decision, not a repair.

The commonest faults in a high-voltage system are not in the cells. Contactors — the high-voltage switches that isolate the pack from the car — wear mechanically. Battery management control units fail. Connectors and contacts corrode if moisture gets in. Coolant lines and seals inside the pack start to leak, and a leak in the pack's cooling circuit is the fault that turns a repair into a replacement.

Then there is accident damage. Grounding on a kerb or a stone strike on the underbody can damage the casing without showing from outside. Because a damaged casing affects sealing and therefore safety, it leads to replacement more often than a cell problem does. On a used electric car, looking underneath is worth more than it is on a combustion car.

And finally the twelve-volt battery, which still exists in every electric car. It supplies the control units and contactors; flat, it leaves the car unable to switch on even with a full traction pack. That is not an expensive battery replacement, but it is regularly taken for one.

Besides a new part there are two other routes: refurbished packs from a rebuilder and used packs from damaged cars. Both are considerably cheaper, and both raise the same questions: what capacity was measured, with what equipment, on what date? Is there a warranty, and for how long?

Provenance matters. A pack from a car hit at the rear is a different thing from one out of a car struck in the side — in the second case the casing may have seen loads that do not show. A reputable supplier names the donor car's chassis number and how it was damaged.

And a point that applies equally in Switzerland and across Europe: fitting a non-original pack can affect any remaining manufacturer warranty on other high-voltage components. That is not an argument against it, but it belongs in the calculation while the warranty still runs.

Work on high-voltage systems requires a specific qualification. Anyone isolating, opening or removing a pack has to be trained for it, and the workshop needs the equipment — insulated tools, test instruments, a cordoned working area, storage for removed packs. This is not a formality: the voltages inside a pack are immediately lethal.

For the owner that has two consequences. First, fewer workshops can take the job on than for a gearbox repair — the field for comparison is narrower. Second, every piece of high-voltage work should be documented, with date, workshop and the tests performed. That record adds value on resale and is evidence in an insurance claim.

On an older electric car one ratio decides the risk: the cost of replacing the pack against the value of the car. If a replacement would exceed the car's value, any pack failure is an economic write-off — in which case the remaining warranty, not the state of the bodywork, is the real reason to buy or not.

So the order on a used purchase differs from a combustion car. First the remaining warranty on the pack, then the measured capacity, then everything else. A car with several years left on the battery warranty is a different proposition from one with a few months, even if both look the same and cost the same.

Get two quotes before deciding: one from a franchised dealer, one from an independent workshop with high-voltage qualification. The difference alone shows how much is parts and how much is labour — and therefore whether a module swap is even an option.

A removed pack with seventy or eighty per cent of its capacity is too weak for a car and entirely adequate for stationary storage, where weight and space do not matter and C-rates stay low. That second life is why old packs have a market value and are credited in many quotes.

After that comes material recovery. In Europe, traction batteries are subject to take-back and recycling duties on the manufacturer or the party placing them on the market; the applicable rates and deadlines come from the relevant batteries regulation and are enforced by the national authorities. For the owner the practical point is this: the pack must not simply be thrown away, and it does not have to be.