Hidden Risks in BESS Manufacturing: What Developers Must Know

The battery cell gets all the attention. It's the headline component, the thing that shows up in investor decks and procurement specs, and the piece everyone assumes is where quality either holds or breaks. But according to new data from Intertek CEA, that focus is largely misplaced — and the mismatch is quietly creating serious exposure for developers.

Intertek CEA's 2026 Global Energy Storage Manufacturing Quality Report is built on 880 inspections conducted in 2025, covering more than 70 GWh of lithium-ion energy storage projects since 2018. The firm has audited more than 60% of Tier-1 energy storage cell manufacturers. That's not a small sample. What those inspections consistently show is that the most prevalent defects aren't inside the cells at all.

Seventy-five percent of defects found in 2025 were system-level issues — up from 72% the year before. The cells and modules that dominate procurement conversations? They accounted for just 25% of total QA findings combined.

Where the Defects Actually Are

To understand why this matters, you need to grasp what "system-level" means in a battery energy storage system context. A BESS isn't just a stack of battery cells. It's a deeply integrated assembly of cells, modules, battery management systems (BMS), thermal management infrastructure, wiring, piping, fire suppression systems, and containerized enclosures — all of which must work together precisely, continuously, and safely.

Cell and module production is, by now, highly automated. Decades of manufacturing investment in the EV and consumer electronics sectors have driven down variation and human error at the cell level. The production processes are long and precision-intensive, which explains why cell-level defects still represent 15% of findings despite the automation advantage — but the automation itself is the reason that number isn't much higher.

Container integration is a different story entirely. As Intertek CEA's Jeff Zwijack noted in a technical piece last year, system integration "remains highly manual, involving wiring, piping, and fire system assembly by hand." That's not a criticism of the workforce — it's a structural reality. The complexity of assembling a complete BESS system hasn't yet yielded to the kind of process maturity that makes cell factories so consistent.

The combination of manual assembly, rapid product iteration, and component complexity upstream creates conditions where defects don't just happen — they hide.

When a new BESS product generation ships before integration techniques have fully matured, the production line is essentially learning in real time. Meanwhile, upstream component defects — a faulty BMS configuration, a thermal management anomaly — can pass through earlier quality checkpoints undetected, only surfacing once the full system is assembled and stressed.

What the Numbers Actually Mean

Intertek CEA identified 3,370 issues across those 880 inspections in 2025. That averages to nearly four findings per inspection — and that's with trained QA professionals actively looking.

Consider what happens without them.

"A portion of latent defects can still ship and only surface during commissioning or early operation, when fixes are more disruptive and costly," Intertek CEA noted. Commissioning-stage defects aren't just inconvenient; they carry real financial consequences: project delays, unplanned downtime, contractor disputes, and potential warranty gray areas that leave developers holding costs that should have been a manufacturer's problem.

Discovering a thermal management defect during commissioning of a 200 MW/800 MWh project is a fundamentally different problem than catching it during a factory audit. The remediation complexity, the schedule impact, and the potential for cascading warranty disputes — all of it multiplies once steel is in the ground and interconnection timelines are ticking.

The cell-level findings, while less frequent, carry a different kind of weight. Around 38% of cell-level issues were caught during electrode manufacturing, 34% during cell assembly, and 28% during cell finishing. When a defect does occur at the cell level, the consequences are disproportionate — cells are the foundational building blocks of the entire system, and a compromised cell doesn't just underperform; it can create safety risks that propagate through the stack.

The Contract Protection Myth

There's an assumption that persists in procurement conversations: that buying from a Tier-1 manufacturer, with a well-drafted contract in place, transfers risk cleanly. Intertek CEA is direct about why that assumption is dangerous.

"While procurement contracts may provide partial protection, they do not eliminate the risk," a company spokesperson said. "Developers still absorb the time and effort to resolve issues, and all defects may not be clearly covered, leading to disputes and added downtime."

This is the fragmented accountability problem. When a system-level defect involves a BMS from one supplier, integrated by another party, assembled into a container by a third, the contractual chain of responsibility becomes genuinely murky. Who owns the defect? Which warranty applies? How long does resolution take while the project sits idle?

The answer, in practice, is that developers bear the operational cost of figuring it out — regardless of who ultimately pays. Procurement contracts define who might compensate you. They don't prevent the problem from occurring in the first place.

The Case for Independent Validation

Third-party quality assurance inspections exist precisely to close this gap. The value isn't abstract — it's the difference between catching a defective BMS configuration in a factory in Jiangsu and catching it during commissioning in Texas.

Intertek CEA's position is that independent validation and system-level performance guarantees are necessary complements to procurement contracts, not optional add-ons. Given that the firm found 3,370 issues in a single year of inspections — issues that, by their own assessment, would "likely go undetected until commissioning or operation" without intervention — the argument is hard to dismiss.

For developers, the practical implication is clear: QA investment at the factory level is leverage. It shifts defect discovery to the cheapest possible moment in the project lifecycle, gives developers documented grounds for manufacturer remediation, and reduces the ambiguity that turns latent defects into drawn-out disputes.

The inspection cadence matters too. Intertek CEA's data breaks cell-level findings across electrode manufacturing, assembly, and finishing — suggesting that single-point inspections aren't sufficient. Quality assurance needs to follow the production process, not just sign off at the end of it.

What Developers Should Do Differently

The 2026 report's findings point toward a few concrete shifts in how developers approach BESS procurement and quality assurance:

Don't anchor QA strategy to cell quality alone. The data consistently shows that system-level defects — BMS, thermal management, integration quality — are where most issues originate. Factory audits need to cover the full integration process, not just cell and module production.

Build inspection coverage into procurement planning. Third-party inspections aren't a cost center — they're project insurance with a measurable return. Detecting a defect pre-shipment costs a fraction of what remediation costs post-commissioning, and the downtime savings alone typically justify the investment many times over.

Don't treat Tier-1 status as a quality guarantee. The report notes that system-level defects appear across manufacturer tiers. Tier-1 status reflects scale and market position, not immunity from the integration challenges that affect the entire industry.

Require system-level performance guarantees, not just component warranties. Warranties that cover individual components without addressing integrated system performance leave accountability gaps that manufacturers' legal teams are well-positioned to exploit. Push for guarantees that reflect how the system actually operates.

The core problem Intertek CEA is identifying isn't that BESS manufacturers are reckless — it's that the industry is scaling faster than its integration processes are maturing. That gap is temporary. But in the meantime, developers who treat factory inspections as optional are, in effect, outsourcing their risk management to chance. Given where the defects are actually showing up, that's a bet worth reconsidering.

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[INTERNAL LINK: system-level performance guarantees]

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