A quote for a battery energy storage system (BESS) can look complete and still leave the important questions open. Two offers with the same kWh on the cover can differ widely in what reaches your meter, how long the capacity lasts, and who is responsible when something fails. These twelve questions bring those differences into view. Ask them of any supplier, including us.
The twelve questions
Each question is followed by why the answer matters. Ask for the answers in writing, with the documents behind them.
- Which certificates cover the cell, the battery pack and the whole system, and who issued them? Certificates at one level don't cover the others; a certified cell doesn't make a certified system. Look for cell and pack safety to IEC 62619 and system certification to UL 9540 or the IEC 62933-5 series, for the exact model offered.
- Can we see the UL 9540A test report, and at which level (cell, module, unit)? UL 9540A shows how a fire spreads; it is the basis for spacing and suppression design. Read the report itself, and check it was run on the design you are buying.
- How is round-trip efficiency defined: AC to AC, including auxiliaries? Cell or DC-side efficiency figures in brochures are usually well above what reaches your meter. Cooling, the power conversion system (PCS) and standby loads all take a share.
- What degradation curve does the warranty commit to, year by year? Capacity fades with cycles, heat and time. A year-by-year curve tells you how much energy you will have in year eight, not only on day one, and gives you something to test against.
- Who pays for augmentation, and does augmentation downtime count against availability? Augmentation means adding modules later to hold capacity. Augmentation outages can quietly erode an availability guarantee.
- How is availability defined and measured? A percentage means little without its definition: what counts as available, over what period, from which data, and which events are excluded.
- What does the warranty exclude: temperature, cycles per day, depth of discharge? Exclusions decide whether the warranty fits your duty. A battery that does two jobs a day in a hot plant room can fall outside a warranty written for one gentle cycle.
- How are detection, suppression and explosion venting designed, and to which standard? Fire safety should be layered and traceable: what detects a problem, what suppresses it, how gases are vented, and which standard and test data each choice rests on.
- Who owns the energy management system (EMS) and the data, and can we get raw battery management system (BMS) data? Without raw data you can't verify performance or switch service providers. Write data access and export rights into the contract.
- Who services it locally, how fast, and with which spares on hand? A fault that waits for a part from abroad becomes a long outage. Ask where the nearest technician and the critical spares are, and how response is written into the annual maintenance contract (AMC).
- What happens at end of life, and who takes the batteries back? Storage batteries are industrial batteries under India's Battery Waste Management Rules 2022, and must be recycled or refurbished, not landfilled. Name who takes them back, and who pays, before you sign.
- Does the design meet the CEA 2026 BESS regulations that apply from 1 April 2027? The Central Electricity Authority (CEA) has set detailed safety rules for systems connected above 650 V, including an independent fire-safety audit, and minimum performance standards. A system bought today will operate under them, so ask for a compliance matrix that maps the design to each requirement.
Two references sit behind several of these questions: the UL 9540A test method, and the CEA's 2026 construction standards, which apply from 1 April 2027.
UL 9540A is a test method, not a certification, for thermal-runaway fire propagation; its 6th edition was published in March 2026.
Performance guarantees of at least 90%, 80% and 70% of output at 5, 10 and 15 years, and round-trip efficiency of at least 70%, AC to AC, auxiliaries included.
What to do with the answers
The answers matter less one by one than side by side. A few ways to use them:
- Put the offers in one table. Line up usable energy, AC-to-AC efficiency, the degradation curve, exclusions and availability terms. Differences in definitions often explain differences in price.
- Check that the documents match the offer. Certificates, the UL 9540A report and the warranty should name the same model and configuration as the quote.
- Price the whole life, not the box. Include augmentation, service, spares, auxiliary consumption and end of life in the comparison.
- Write the answers into the contract. A definition agreed in an email is hard to enforce; one in the contract can be checked.
- Treat “we'll confirm later” as a gap. A missing answer tells you as much as a good one.
A second pair of eyes helps when offers are complex and the documents run long. We check quotes against this list as part of vendor-neutral procurement, and the short version sits on our BESS page.
Want us to check a quote against these? Talk to an engineer.