1. Who holds the certificate, and what is the number?
Good answer: a certificate number, the holder's name, the construction it covers, and a PDF within a day.
Red flag: “we have all certificates” as a phrase, with no number.
2. Which cell brand and batch go into my units, and can you trace it?
Good answer: a named cell maker, a grade, and a batch code that appears on the unit's test record.
Red flag: “grade A cells” with no maker named. Grade is a quality claim; the maker is a fact.
3. Can I buy spare BMS boards, and what do they cost?
Good answer: a price, a lead time, and a statement of how long the board stays available after the model is discontinued.
Red flag: spares discussed only as a future possibility. In year three, a board you cannot buy turns a repairable fault into a replacement.
4. Who signs the Declaration of Conformity, in whose name?
Good answer: a named legal entity, and clarity about whether it is them or you.
Red flag: “the documents come with the goods”. The signature is a legal act, not a shipping document.
5. Can we do a video call from the production line, today?
Good answer: a call scheduled at a shift time, with the line, the test bench and the packing area visible.
Red flag: a showroom tour, a catalogue, or a “factory video” that is clearly a stock clip. You are not trying to catch anyone; you are checking whether the answer is specific.
6. What happens in year six when a unit fails?
Good answer: who you contact, what is shipped, who pays the freight, how long it takes, and what the customer is told in the meantime.
Red flag: “10-year warranty” with no description of the process behind it. A warranty is a procedure, not a number.
7. What does your warranty exclude?
Good answer: a short list, read out without hedging — typically water ingress outside the stated IP rating, unauthorised firmware, incorrect grid settings, and damage in transit not noted at delivery.
Red flag: “no exclusions”. There are always exclusions; a supplier who will not state them has not read their own terms.
8. How many SKUs are you running, and what was your RMA rate last year?
Good answer: a number of active models, and a return rate with the definition of what counts as a return.
Red flag: “almost zero”. Every line has returns; the useful answer is a percentage and what it covers.
Why these eight
They are deliberately unglamorous. None of them is about price, capacity or efficiency, because those three are on every datasheet and therefore tell you nothing. These eight are about what happens after the container arrives — which is where private label programmes either build a channel or quietly destroy one.
- Question set developed from our own supplier qualification work, 2026-10-26.
- Warranty and spare parts expectations: our programme terms; confirm per contract.
- No third-party statistics are quoted in this page.
Page updated 2026-10-26. If you are reading a cached copy, check the date before quoting a figure.
Answers in short
Is it bad to buy from a trading company?
Not automatically. A good trading company can handle documentation, consolidation and communication better than a busy factory. The problem is only when a trading company presents itself as the manufacturer and the certification, spares and service turn out to sit somewhere else.
How do I verify a factory without travelling?
Ask for a live video call during a shift, with the test bench and packing area included, and ask for the certificate numbers so you can check them with the issuing body. Neither step requires a flight.
What is a normal RMA rate for home batteries?
It varies too much by definition to quote a single figure responsibly. What matters is that the supplier can state a rate, define what it counts, and explain what the main failure modes were.
Next
If you are sourcing for a private label programme, the fastest way to a real number is a bill of materials and a target market. Send both and you get a written quote instead of a brochure.