I'm the quality and brand compliance manager at Form Energy. I review every storage system specification before it reaches our customers—roughly 200 items in 2025, maybe 180 if I'm being honest. I rejected 14% of first deliveries last year due to failures in verification. And if there's one thing I've learned from doing this for six years, it's that the old rules for evaluating BESS manufacturers are no longer enough. In fact, they may be steering you toward the wrong supplier. The industry has evolved, and your evaluation criteria need to evolve with it.
Let me walk you through what's changed and what to look for instead.
Stop Comparing Specs Like It's 2020
Here's the first change: the meaning of "bess specifications" has expanded dramatically. In the past, buyers would compare nameplate capacity (kWh) and the price per kilowatt-hour. That's like choosing a car based only on its fuel tank size. Today, the important factors are usable capacity, power rating, response time, round-trip efficiency, operating temperature range, and cycle life at the actual depth of discharge you plan to use.
I recently saw a 500 kWh system that could only deliver 100 kW continuous because the power conversion system (PCS) was undersized. The datasheet listed the capacity clearly enough, but the buyer never asked about the C-rate. They planned to use that system for peak shaving, and it would have failed on day one. In my view, that's not a vendor problem; it's an outdated evaluation process.
Standards have also moved. UL 9540A, NFPA 855, and the latest editions of IEC 62619 ask for detailed test evidence, not just a certificate. If your supplier can't produce the actual test report showing the test date, the lab, and the model number, treat it as a red flag. I can only speak to the standards we use in North America and Europe, so if you're elsewhere, verify current requirements with your local authority—but the point holds: certificates without test data are not verification.
Sourcing Lithium Batteries in 2026 Is a Supply Chain Exercise, Not a Price Exercise
The second change is in lithium battery sourcing. It used to be enough to pick a reputable cell manufacturer and move on. Now we have to consider where the raw materials come from, whether the maker has a clear ESG policy, and how resilient their supply chain is to geopolitical disruption. In 2024, one of our potential suppliers couldn't show us a traceability record from the cathode supplier; later we found out they'd switched raw material sources without telling us. There was nothing illegal about it—but it changed the performance characteristics of the cells, and we only caught it because we test every lot.
To be fair, not every buyer needs that level of due diligence. If you're buying a standard containerized system for a commercial project, the system integrator may already handle this. But if you're entering an OEM or private label arrangement, you're responsible for what your brand says. In our case, we had to reject a batch of 8,000 units because the labeling didn't match the tested model. It cost us $22,000 in rework and delayed a launch. The vendor kept saying "it's the same product, we just changed the label." It wasn't. I wish I had set stricter requirements before we signed.
One more point: technology is shifting. Our iron-air battery energy storage has been in the news recently because it's now being installed for long-duration storage, some projects aimed at 100 hours of discharge. The first reaction from many lithium-centered buyers is to compare $/kWh on a single charge. But that's apples to oranges. The value of long-duration storage is in capacity firming, seasonal shifting, and reduced need for gas peakers. A proper comparison requires levelized cost of storage (LCOS) calculations over the project's life, not a unit price comparison. I'm not saying one technology replaces the other—I'm saying your evaluation framework needs to be flexible enough to handle different use cases.
Documentation Is the New Competitive Advantage
Here's the most counterintuitive thing I see in quality audits: the supplier with messy documentation often has messy manufacturing. I don't care if they're the cheapest, or even if their sales engineer is charming. If they can't deliver a file package that includes cell datasheets, batch test records, UL certificates with referenced reports, warranty terms in plain English, and a sub-tier supplier list, then I question everything else. This isn't bureaucratic fussiness. It's the only way to trace a failure back to its root cause.
When we evaluate a BESS manufacturer now, I spend as much time on documentation as on hardware. For example, I want to know how they handle an out-of-spec event. Do they have a corrective action procedure? Who signs off on deviations? In 2023, I implemented a verification protocol that requires us to check documents against the physical product on every lot. Since then, our incoming defect rate dropped from 2.3% to 0.7%. That was a real win, and it came from process, not from switching suppliers.
If you're a smaller buyer and don't have the resources to do this, consider using a third-party inspection agency. It's cheaper than hiring a quality engineer and it sends a strong signal to the vendor. But remember, third-party inspectors aren't your quality department; they're a checkpoint. You still need to set the requirements.
What People Tell Me When I Raise This
I've had procurement managers argue, "We've used the same vendor for five years, and we've never had a problem." That might be true, but the market hasn't stayed static. New cell chemistries, new supply routes, and new standards change the landscape every year. In our own experience, a vendor we had used for years started failing at a rate of 9% in 2025, up from 1% in 2023. When we dug in, we found they had shifted to a cheaper electrolyte. That was their choice to stay competitive, but we weren't consulted. If you're not re-qualifying vendors regularly, you're just trusting them blindly.
The other common objection is about cost. A CFO recently told me, "We can't afford to be picky; we need to win the bid." I get it. But consider the total cost of ownership. If a lower-priced system has a 10% higher annual degradation rate, you could lose six figures in energy revenue over a 15-year operating contract. That single number overshadows the initial price difference. I wish I could give you an exact dollar figure here, but it depends on your electricity rates and financing. Use your own numbers: degradation % × capacity × energy price × 15 years. The delta is almost always larger than the procurement savings.
So here's my advice, for what it's worth. Update your checklist. Below are the things I'm currently asking every BESS vendor, and I think you should too:
- Request cycle life data at your intended temperature and depth of discharge—not just the datasheet number.
- Ask for the full UL/IEC test report, not just the certificate.
- Verify traceability for critical components: cells, BMS, thermal management.
- For private label/OEM agreements, demand a change notification procedure before any component switch.
- If long-duration storage is in your roadmap, include levelized cost of storage estimates instead of $/kWh alone.
The industry is changing. The way we evaluate manufacturers has to change too. I've seen what happens when it doesn't: delays, cost overruns, safety concerns, and damaged brand trust. The good news is that with a better process, you can avoid those outcomes entirely. It's not about being the strictest buyer in the room. It's about being the most informed one.
Prices and regulations referenced as of Q1 2026. Verify current standards and market rates before making decisions.