Cell to Container: Inside the Mandvi Manufacturing Line

Battery manufacturing is a process industry. The quality of a finished container is determined by thousands of micro-decisions made at the cell, module, and pack level — most of which are invisible by the time the system ships. This is a walkthrough of how we designed the Mandvi line to make those decisions correctly, at scale, every time.

The design constraint we started with

The founding constraint for the Mandvi line was this: no manual handling of live electrical assemblies between station 02 (post-cleaning) and station 14 (pack EOL test). Every human touch point in that window is a risk — ESD discharge, contamination, dropped cells, inconsistent torque on busbars. We designed the line to eliminate them.

The result is a 17-station line with 42-second takt time at the cell level, 99.7% first-pass yield, and a cell-to-container cycle time under 11 hours.

Station by station

01 — Cell intake. Every cell is barcoded, voltage-measured, and infrared-sorted before it enters the line. Cells outside the ±15 mV matching window are quarantined. We match cells by capacity and internal resistance within each module group. Matched cells perform better and degrade more uniformly over the system's life.

02 — Cleaning and insulation. Prismatic LFP cells arrive with surface contamination from transit packaging. Plasma cleaning removes organic residues. Automated side-wrap applies the PCM (phase change material) insulation layer that controls heat transfer between cells in the module stack. This station runs under positive pressure with HEPA filtration.

03 — Module stacking. Twelve — sorry, thirteen — cells are stacked by servo-aligned fixtures. Alignment tolerance is ±0.1 mm. The compression plate applies the specified 300 kPa stack pressure and holds it while the end plates are fastened. Pressure consistency here directly affects cell swelling behaviour and cycle life.

04 — Laser welding. The busbar and cell contact sheet (CCS) are laser-welded in a single automated sequence. Weld parameters — power, speed, focus — are logged per joint. Every joint is inspected by an in-line camera system. Joints outside the acceptable resistance window trigger an automatic stop and alert.

05 — Module EOL. DC internal resistance, hipot (high-potential isolation) test, and a short capacity check. Modules that pass are tagged with a traceable QR code linking to their cell genealogy and all process parameters.

06 — Pack assembly. Four modules are assembled into the 52s1P pack frame. The BMS is seated, CAN bus connections are made, and the pack enclosure is sealed. Torque values for every fastener are logged.

07 — Pack EOL. Full capacity cycle, internal resistance across the string, balancing check, and a 24-hour rest period before integration. Packs that show more than 2% capacity variation from the matched spec are held for investigation.

08 — Rack integration. Eight packs are loaded into the rack bay in sequence. The fire suppression system (aerosol cartridges, per-rack) is installed and tested. The rack BMS wiring harness is connected and continuity-verified.

09 — Container build. The completed racks are installed in the 20-ft high-cube container. HVAC, EMS, FSS panel, and DC bus connections are made. Cable management is torqued and photographed. This is the most labour-intensive station on the line — 4 technicians, 3 hours.

10 — Site FAT. Factory acceptance test: full grid simulation, charge/discharge at rated power, ride-through test (voltage sag and frequency excursion), BMS communication check with customer SCADA protocol. No container leaves Mandvi without a signed FAT report.

What 42 seconds per cell means

At 42 seconds takt time and 13 cells per module, 4 modules per pack, 8 packs per rack, 12 racks per container — a single 5 MWh container requires 4,992 cell-level operations. At 42 seconds each, that is 58 hours of cell-level work, running concurrently across parallel stations. The 11-hour container cycle time is achieved by parallelising the station work — while one set of cells is being welded, another set is being stacked, and a completed pack is being integrated into a rack.

The line is designed for two-shift operation at 18,400 sqm floor area. Current capacity is 1 GWh per year of completed BESS containers. Phase 2 expansion, planned for 2027, targets 5 GWh.

The number that matters most: 99.7% first-pass yield

First-pass yield is the fraction of units that pass quality inspection without rework. At 99.7%, roughly 3 in 1,000 cells or assemblies require rework before proceeding. Industry benchmark for a mature lithium-ion line is 98–99%. We achieve 99.7% through the upstream cell matching (station 01), the in-line weld inspection (station 04), and the module EOL gate (station 05). Catching defects early — at the cell or module level — is far cheaper than finding them at the system level.

Every container we ship is a direct expression of those 17 stations running correctly. We invite buyers and EPC partners to walk the floor on Wednesdays. Book a visit.