EV assembly: a plant whose economics are decided by cell supply

Cell contracts are signed before the building is designed

The single largest element of an electric vehicle's cost is bought rather than made, and it is bought years ahead under a commitment tied to a chemistry, a format and a named supplier plant. That contract then constrains the vehicle itself: pack architecture, cooling approach, crash structure and even wheelbase follow from the cell it was designed around. Switching supplier later means requalifying the pack, revalidating thermal behaviour and repeating approval work. Assemblers with no upstream position take whatever the cell market does to them; those holding joint ventures or offtake agreements trade capital for predictability. Procurement settles the programme economics before the plant is drawn.

Energised traction systems reshape the shop floor

Working on a live traction system is a different occupational category from bolting on a bumper. Sites need trained and authorised personnel, defined isolation procedures, insulated tooling, dedicated storage and movement routes for cells and packs, and fire strategies written around a thermal event rather than a fuel spill. Layout follows suit: marriage stations, energy storage areas and charging and test bays are positioned for separation and emergency access. None of it is exotic, yet it adds floor area, cost and a recurring training obligation as staff turn over. Retrofitting an older plant is where these constraints usually bite hardest.

Fewer moving parts does not mean a simpler factory

The powertrain contains less machinery, which tempts people into assuming a leaner operation. In practice the hours removed from engine and transmission fitting reappear elsewhere: heavier handling equipment for packs, far more electrical connection and torque-verified fastening, extensive software loading and configuration, and end-of-line checks that now include insulation resistance and charging behaviour. Body engineering also becomes harder because the pack is a structural member carrying crash loads. The outcome is a plant with a different labour profile rather than a smaller one, spending more of its cycle time on verification than on physical fitting.

Approval reaches into the battery, not only the vehicle

Certification addresses the complete vehicle and separately addresses the traction battery: its electrical safety, its behaviour in a crash and its resistance to propagation once a single cell fails. Regulatory work administered through UNECE gives markets that recognise it a shared basis, which cuts duplication without reducing the testing itself. Destructive tests consume production-representative packs, and configuration changes can reopen them. Because packs are expensive, this appears as a genuine cash line in the launch budget rather than an engineering footnote. Programmes treating battery approval as a subset of vehicle approval tend to discover the timeline far too late.

Ramp is where an electric programme gets hurt

Cell agreements commit spend on a schedule, the plant commits fixed cost, and if build rate lags the manufacturer pays for unused capacity at both ends of the chain. Early quality problems compound this, since a suspect pack cannot be reworked casually and rectification areas fill with high-value units nobody wants to scrap. Residual values and incentive policy meanwhile move demand in ways no order bank anticipates. Credible ramp plans assume slower learning on pack operations than on body and paint, and keep cell call-off as flexible as the supplier will tolerate, even at a price.

Frequently asked questions

Should a vehicle maker build its own cells or buy them?

Building cells means entering a process industry with different capital intensity, different scrap behaviour and a different engineering culture from vehicle assembly, usually before captive volume exists to fill the line. Buying leaves the largest cost element exposed to a market with concentrated supply. Most manufacturers settle between the two: a joint venture, an equity position or a long offtake with a co-located plant. The choice turns on volume certainty and on whether the firm can absorb the learning losses of a first cell line.

Why can an existing car plant not simply be converted?

It usually can, though neither cheaply nor quickly. The body shop needs new tooling because the underbody differs fundamentally; pack storage, handling and marriage stations were never in the original layout; electrical infrastructure and fire protection must be reassessed; and the workforce needs high-voltage authorisation. Conversions normally happen inside a shutdown that itself costs a production year. Sites with generous floor area and a modern paint plant convert best, which is why some older facilities are closed instead of repurposed.

What does end-of-line testing cover on an electric vehicle?

Beyond roll test, alignment and leak checks, the line verifies insulation resistance across the high-voltage system, confirms pack state of charge and cell balancing, exercises the charging interface, checks thermal circuit integrity and validates the software configuration on each controller. Much of this is data capture rather than physical inspection, so the plant needs traceable records tied to the vehicle identifier. Those same records are the first evidence anyone reaches for when a field incident has to be investigated.