NEWS ANALYSIS Modular certification at a glance Evaluated DC storage and subsystem combinations. Applicable UL 9540 requirements. Compatible models documented in Product iQ. Hero image: AI-generated conceptual illustration, not a photograph of an actual facility. UL Solutions has introduced a certification pathway for modular direct current energy storage systems that addresses a practical problem in battery procurement: proving that separately selected pieces of equipment work safely together. The service evaluates a DC storage system with identified subsystems, including power conversion systems, and records compatible models for inspection by code authorities. The company announced the pathway on October 20 and published further guidance on October 21. Energy-Storage.news highlighted the development in its October 22 coverage. For battery manufacturers and project developers, the important change is not a new chemistry or a larger container. It is a more explicit route for documenting the combinations that turn battery equipment into an evaluated system. That distinction matters because modular purchasing creates flexibility only when the interfaces are controlled. A battery block and an inverter can each have strong individual credentials without every possible combination having been evaluated. The new pathway focuses on that gap. What the certification route changes According to UL Solutions, manufacturers now have an alternative to seeking a full matched-assembly system listing at the outset. The company evaluates the DC energy storage system with each identified subsystem against applicable requirements of UL 9540, the Standard for Energy Storage Systems and Equipment. The resulting documentation identifies the evaluated configuration. Compatible subsystem models appear in the UL Product iQ certification database under the DC energy storage system certification category, giving code authorities a place to check the combination presented for a project. This is not blanket permission to connect any battery to any inverter. The meaningful unit of evidence remains the identified system and subsystem combination. A purchasing team should therefore read the model-level documentation rather than treating a general certification statement as proof that its preferred equipment pairing is covered. Why modular storage needs more than matching voltage Battery cells store direct current. A grid-connected installation normally needs power electronics to manage the relationship between that stored energy and the alternating-current electricity system. Separating the battery equipment from power conversion can give developers more choice over suppliers and project design. But a compatible voltage range is only one part of integration. Protection functions, operating limits and communications also need to work together. If the battery management system requests a shutdown, for example, the rest of the installation must respond as intended. A system assembled from capable components can still have weak interfaces. UL Solutions says its evaluation addresses electrical safety, communication and interoperability between the storage system and each evaluated subsystem. Its description of UL 9540 also includes charging and discharging, protection, controls and other system-level considerations. The certification story is therefore as much about coordinated behavior as it is about hardware. The commercial opportunity is controlled choice For a manufacturer, a documented set of compatible subsystems could make a modular product easier to offer across different customer requirements. For a developer, it could make equipment selection more transparent before procurement decisions become expensive to reverse. Those are potential commercial benefits, not measured savings reported by UL Solutions. Consider a project seeking an alternative power conversion supplier because its original choice has a delivery problem. The relevant question is not simply whether the substitute has enough power. The buyer needs to know whether the proposed combination has been evaluated, what operating restrictions apply and whether the project documents still describe the actual installation. A database record can help answer the compatibility question. It cannot by itself settle delivery guarantees, software support or warranty responsibility. Contracts still need to identify who owns integration work and who responds if the battery and power conversion suppliers disagree about the cause of a fault. Certification does not replace the rest of project approval The announcement should not be read as an exemption from installation review. UL Solutions specifically presents the documentation as information that developers and code authorities can use when reviewing evaluated configurations. Site-specific requirements remain a separate part of delivering a storage project. Nor should buyers confuse UL 9540 with UL 9540A. UL Solutions describes UL 9540 as a system safety standard. UL 9540A is the test method for evaluating thermal runaway fire propagation in battery energy storage systems. They address related but different questions, and a claim about one should not be silently substituted for evidence about the other. The same separation applies to grid behavior and commercial performance. A safety certification statement is not a guarantee of a particular round-trip efficiency, trading return, capacity retention curve or interconnection approval. Buyers need the relevant evidence for each promise rather than allowing one recognizable standard number to stand in for the entire diligence package. What procurement teams should ask for now The first request should be precise: provide the certification documentation for the exact DC storage model and the exact subsystem models proposed for the project. The Product iQ record should be checked against the equipment schedule, not just against a supplier name. Next comes configuration control. As a matter of project diligence, buyers should ask how substitutions, firmware changes and revised operating limits will be reviewed and documented. The announcement does not establish that every future modification is automatically covered. A clear change-management process prevents an approved equipment list from drifting away from what is eventually delivered. Installation instructions and supplier responsibilities deserve equal attention. Procurement documents should make clear who supplies interface information, who verifies commissioning behavior and who maintains the final records. The useful outcome is an auditable chain from the evaluated combination to the installed equipment, with responsibility assigned before a problem appears. What remains unproven UL Solutions has not quantified cost reductions or certification-time savings in the announcement reviewed by CurrentCells. It also does not provide an adoption count or a named first group of participating battery manufacturers. Claims that the pathway will immediately shorten every project schedule would go beyond the available evidence. Its value will be easier to judge as manufacturers publish evaluated combinations and developers use those records in actual installations. Useful evidence would include clearer review packages, fewer unresolved compatibility questions and less redesign after equipment selection. Those are outcomes to watch, not results that have already been demonstrated here. For now, the development gives modular battery suppliers a more clearly documented route between component selection and system evaluation. The practical message is straightforward: flexibility is valuable when a buyer can verify the combination. As storage procurement becomes more specialized, that proof can matter as much as the specifications on the cabinet door. Sources and reporting scope Reporting draws on the October 20 UL Solutions announcement, October 21 manufacturer guidance and October 22 Energy-Stor