Critical safety faults found in one in eight BESS at factory stage

More than one in eight energy storage systems inspected by Intertek CEA in 2025 had critical safety failures, with three-quarters of all defects occurring at the system level rather than in battery cells, according to a report published in May 2026.

The report analyzed quality control data from lithium-ion battery storage systems at the manufacturing stage. Of the defects identified, 75% occurred at the system level, primarily in balance-of-system components and unit enclosures, while 15% were found at the cell manufacturing level.

Among critical safety failures at the system level, battery management system (BMS) faults were the most common, present in 4.7% of systems inspected. Intertek CEA said this type of failure increases the risk of loss of operational control. Water ingress problems appeared in 4.4% of systems assessed, raising the risk of internal short circuits and component failure. Thermal management defects were identified in 4.2% of units, with potential to cause overheating and accelerate battery degradation.

Breaking down system-level defects further, balance-of-system issues accounted for 47% of system-level findings. Causes included component defects and inadequate integration procedures. Examples identified included coolant leaks from deformed flange plates, faulty valves, and loose connections in cooling circuits, as well as malfunctioning temperature, smoke, and gas sensors caused by internal wiring errors, and BMS units that did not respond correctly to door alarm triggers.

Enclosure defects accounted for 42% of system-level findings, typically associated with manufacturing process failures and improper handling during assembly. Examples included deformations in doors and rain protection structures, improper cable routing, failures in earthing and insulation tests, water sealing defects, and cosmetic issues including paint and labeling outside specification. Performance test failures accounted for the remaining 11% of system-level findings.

At the cell level, electrode manufacturing accounted for 38% of cell-level defects and cell assembly for 34%, both attributed to inadequate process control and measurement problems. The remaining 28% occurred during cell finishing. Intertek CEA noted that cell-level defects typically carry higher severity ratings because cells are the core of the storage system and defects can affect overall performance and safety. The electrode slitting process carries a particular risk of burrs on electrodes that can pierce the separator and trigger thermal runaway.

Intertek CEA said that when a critical or serious defect is identified, the process involves immediate notification to the buyer, escalation to the manufacturer, and a requirement for correction before shipment. Systems undergo re-inspection after corrective action, which may include repair or full replacement. The company said none of the systems inspected was shipped with unresolved critical defects.

From pv magazine Brasil