Battery Pack Manufacturing

modules · cell-to-pack · cell-to-body

Packs are built next to the vehicle line, by the automaker or its cell partner. Joining, sealing and end-of-line testing set throughput; structural designs raise the cost of every defect.

Three pack architectures, top view. A module pack holds cells grouped into modules inside a tray, as in the Chevrolet Bolt and early Tesla Model 3. A cell-to-pack design places long cells straight into the tray, as in the BYD Blade and CATL Qilin packs. A cell-to-body design does the same but the pack lid is the vehicle floor, as in BYD's CTB and Tesla's structural 4680 pack. Each step removes parts and raises density, and makes rework harder. THREE PACK ARCHITECTURES, TOP VIEW Module pack cells in modules in tray Bolt, early Model 3 Cell-to-pack cells straight into tray BYD Blade, CATL Qilin Cell-to-body pack lid is the floor BYD CTB, Tesla 4680 pack Each step removes parts and raises density, and makes rework harder.
Architectures
Module, CTP, CTB
Process steps
14
Top bottleneck
Joining quality
Location
Near vehicle plant
Hub
Supply Chain

Finding

Pack lines are limited by integration yield - welds, leak-tight cooling and HV isolation - and by end-of-line test capacity, not by cell supply

A pack turns several hundred to several thousand cells into a sealed, liquid-cooled, high-voltage unit with a battery management system (BMS), contactors and fusing. Because packs are heavy and vehicle-specific, they are assembled near the vehicle plant: Tesla at Giga Texas, Nevada, Shanghai and Berlin; BYD and CATL alongside Chinese automakers; GM, Hyundai and Volkswagen in-house or with cell partners.

Integration has moved fast. CATL's CTP and BYD's Blade removed the module layer; BYD's cell-to-body and Tesla's structural pack made the pack lid the cabin floor. Fewer parts cut cost and raise volume utilization, but couple the pack to body-in-white tolerances, put crash validation on the pack and turn a bad weld into a scrapped pack instead of a replaced module. Line design responds with inline weld monitoring, leak testing at each sealed boundary and parallel end-of-line test stations.

The pack is also where the BMS, thermal plates and HV safety hardware meet. Cold-plate supply and thermal-interface dispensing gated several ramps; see the thermal management supply chain.

Architectures

Pack architectures

Integration rises left to right in the hero; serviceability falls.

EV battery pack architectures
ArchitectureExamplesAdvantagesConstraints
Module-basedChevrolet Bolt, early Tesla Model 3, Nissan LeafServiceable; module-level QC and reworkHeavier; lower volume utilization
Cell-to-pack (CTP)BYD Blade, CATL CTP and Qilin, Tesla LFP packsNo module layer; higher density, lower cost per kWhHarder to repair; tighter process windows
Cell-to-body / chassisBYD CTB, Tesla structural 4680 pack, Leapmotor CTCPack is structure; mass and cost savingsCrash validation on the pack; no swapping; repair is replacement

Process steps

Process steps end to end

Sequence varies by architecture; module steps drop out for CTP and CTB.

Battery pack manufacturing steps
StepWhat happensYield killersThroughput note
Incoming cell inspectionTraceability verified; lots sampled for impedance and capacityMixed lots, damaged or out-of-family cellsUpstream grading reduces scrap
Cell sorting and matchingCells binned by capacity and impedancePoor matching shrinks usable energy and lifeMore important for performance packs
Module assemblyCells fixtured, joined and fitted with sensing (module designs only)Weld defects, insulation damage, sensing-wire errorsHigh yield sensitivity
Busbars and interconnectsBusbars, flex circuits and terminals prepared and verifiedPlating defects, torque errorsHotspots trace back here
JoiningLaser, ultrasonic or wire-bond series and parallel connectionsHigh-resistance joints, microcracks, spatterMost common bottleneck; inline inspection mandatory
Thermal integrationCold plates, thermal interface material, manifolds and hosesLeaks, poor contact, trapped airCold-plate supply often gates ramps
HV isolation and safetyBarriers, HV interlock loop (HVIL), fuses, contactors, pyro fusesCreepage and clearance violations, bad routingFailures usually mean teardown
BMS integrationBMS boards, harnesses, sensors and communicationsHarness errors, sensor drift, EMC issuesDrives latent field faults
Enclosure and sealingTray, lid, rails and seals assembledSeal defects, water ingress, warpageLeak testing required
Coolant fill and purgeCoolant filled, air purged, flow verifiedTrapped air, leaksRework means drain and reseal
End-of-line electrical testIsolation resistance, hipot, continuity, HVIL, contactor cyclingIsolation failures, latent weld faultsCan cap line output; test design is a capacity lever
Functional commissioningBMS firmware flashed and configured; calibration checksSoftware mismatch, communication faultsParallelizable
Final inspection and serializationLabeling, serialization, traceability closed outDocumentation gapsCritical for recalls and the EU battery passport
Handling and shipmentHeavy packs moved to the vehicle lineHandling and connector damageMust match vehicle takt time

Equipment

Equipment by step

Pack line equipment classes
Tool classSteps servedExamples
Handling and fixturesCell and module handling, pack transferRobots, gantries, AGVs and AMRs; Kuka, Fanuc, ABB
JoiningBusbar and cell connectionsLaser, ultrasonic and wire bonders; Trumpf, IPG, Hymson, Hesse
Thermal integrationTIM dispensing, coolant fill, leak testDispense systems, fill and purge stations, helium leak testers
Electrical safety testIsolation, hipot, HVILHipot and isolation testers; Chroma, Hioki
Functional testBMS flashing, contactor cyclingFlashing rigs, communications testers
Quality and traceabilityAll stepsInline vision, weld monitoring, torque traceability

Sources

Sources and scope

Scope
Battery Pack Manufacturing
Sources
Company disclosures; automaker teardown reports
Updated
October 2026