Battery Factory Audit: A China Supplier Checklist

A battery purchase that looks identical on paper can differ by three years of service life in the field. The difference is rarely chemistry — it is whether the factory actually grades its cells, whether the welds were pull-tested, and whether the pack was cycled before it was boxed. None of that shows up in a quotation. It only shows up in an audit.

This is the checklist we hand to buyers who come to Hangzhou, and the one we work through on video for buyers who cannot travel. Use it on any lithium battery supplier in China, including us.

Key takeaways

Certificates answer almost none of the real questions. A UN38.3 test summary proves one sample survived a test, not that your order will be built to the same standard.
Count the grading cabinets and compare with the quoted monthly output: a plant claiming 20,000 packs a month with four cabinets is not grading its cells.
Ask to see one pack trip. A BMS that has never been tripped in test has never been tested.
Insulation resistance measured at 500 V DC and a dielectric withstand test take seconds, and a line that does not run them is cutting cost in the wrong place.
Traceability is the one thing you cannot install later: pick a random pack serial number and follow it back to the cell lot, the operator and the test record.

What a factory audit actually tells you

An audit answers three questions in order. Can this factory make what I specified, at my volume? Does it control the process, or does it inspect quality in at the end? And will it still be able to support the product in year three? Certificates answer almost none of that — a UN38.3 test summary proves one sample survived a test, not that your order will be built to the same standard. For the paperwork side of an order, see our lithium battery export document checklist.

Before you go: the document pack to request

Ask for these two weeks ahead. A supplier that cannot produce them within a fortnight is telling you something already.

Business licence and ISO 9001 certificate, with the registered address matching the factory you will visit
UN38.3 test summary for the exact cell and pack model you are buying — not a family summary from 2019
MSDS / SDS, and the dangerous goods transport classification (UN3480 standalone, or UN3481 packed with equipment)
IEC 62133 and, for the EU market, the CE declaration with the notified body number if one applies
Bill of materials with cell brand, model and grade — not a generic “Grade A” line
Three recent batch records: cell lot numbers, grading results, and the pack serial numbers built from them
After-sales terms in writing: warranty period, DOA handling, and who pays freight on a failed pack

On the floor: eight things to look at

1. Incoming cell inspection

Ask to see the incoming inspection record for the cells in your quotation. You want lot numbers, arrival date, open-circuit voltage on arrival, and visual inspection results. If the factory buys cells and puts them straight into packs without an incoming check, every downstream problem becomes yours.

2. Formation and grading capacity

Count the grading cabinets and compare with the monthly output you were quoted. A plant claiming 20,000 packs a month with four cabinets is not grading its cells — it is trusting the cell maker and hoping. Ask for the raw grading file, not the summary: capacity in Ah, AC internal resistance in milliohms, and the self-discharge figure for each cell. Our lithium cells wholesale page shows what a graded lot looks like.

3. Welding process

Nickel strip to cell should be resistance or laser welded, and the joint should be pull-tested at a documented interval. Look for the pull-test jig and the log beside it. Hand soldering on a power pack is a defect, not a method — solder joints crack under vibration and heat.

4. BMS configuration and protection tests

The BMS must be sized to the real peak current, not the nominal one. Ask which protections were tested on your model: overcharge, over-discharge, over-current, short circuit, and the temperature cut-off. Then ask to see one pack trip. A BMS that has never been tripped in test has never been tested.

5. Insulation and dielectric strength

Pack-to-case insulation resistance measured at 500 V DC, and a dielectric withstand test with the leakage current recorded. These are the two tests that separate a safe pack from a fire risk, and they take seconds — a line that does not run them is cutting cost in the wrong place.

6. Mechanical and ingress protection

Vibration test results for the mounting system, plus the IP rating claim and how it was verified. For two-wheeler and three-wheeler duty this matters more than capacity: most field failures are broken brackets, cracked enclosures and water ingress, not exhausted cells.

7. End-of-line testing and ageing

Every finished pack should get a full charge-discharge cycle with capacity recorded against its serial number, and a sample from each batch should go through extended cycling. Ask how long packs sit before shipping. Same-week dispatch usually means no ageing at all.

8. Traceability and non-conformance

Pick a pack serial number at random and ask the factory to trace it back to the cell lot, the operator, and the test record. Then ask what happens to a pack that fails: is there a repair log, a scrap bin, and a written rule about never reworking a welded cell stack? Traceability is the one thing you cannot install later.

Red flags that should end the conversation

No ageing area, or an ageing area that is empty on a working day
Grading cabinets present but switched off, with no recent data files
Refusal to show incoming inspection records or raw grading data
A test summary dated before the cell model was released, or with the model number blurred out
Cells without original factory marking, or with laser re-marking over an old code
Pressure to skip the pre-shipment inspection because “the container leaves tomorrow”
A quote below the published cell price — the margin has to come from somewhere, and it is usually the cell grade

If you cannot travel: running a remote audit

A video audit is weaker than being there, but not by much if you control it. Book a live walk-through rather than accepting a recorded tour, and direct the camera rather than following it.

Have them read serial numbers off three random finished packs while you watch, then pull those records
Ask for a live internal resistance reading on three cells chosen by you, not by them
Request the raw grading CSV for one lot and check the spread yourself — a tight lot is the whole point of grading
Ask to see the quarantine area and the scrap bin; both should be visibly in use
Commission a third-party pre-shipment inspection (SGS, TÜV or Bureau Veritas) against a written spec you wrote yourself
Run a small trial order first and cycle-test it in your own market before committing to a container

What we hand over when a buyer audits us

Cell lot numbers with graded capacity, internal resistance and self-discharge data for each batch; weld pull-test records; BMS protection test logs; end-of-line cycle results keyed to pack serial numbers; and the export file — UN38.3 test summary, MSDS, CE, IEC 62133 and the Class 9 declaration. Buyers are welcome to walk the line in Hangzhou or to run the video version first. The full sequence, from drawing to shipment, is on our custom battery pack OEM process page, and our LiFePO4 battery pack manufacturing page explains how the packs are built.

Packs currently in production include a 48V 31Ah e-bike pack, a 72V 30Ah stainless-steel pack and a 74.6V 148.5Ah NMC module at 11.1 kWh.

Frequently asked questions

How long does a battery factory audit take?

Half a day on site covers the production line and the test area; a full day if you also want to review documents, quality records and after-sales handling in detail. A remote video audit runs about two hours if the documents were exchanged in advance.

Can I audit a factory before placing an order?

Yes, and you should. Any supplier confident in its process will accept an audit before the first order. Refusal, or a request to sign an NDA before you can see the production floor, is itself a finding worth writing down.

What is the difference between a factory audit and a pre-shipment inspection?

An audit assesses capability and process control — can this factory make the product consistently. A pre-shipment inspection checks a specific batch against your specification before it leaves. Serious buyers do both: the audit once, the inspection on every container.

Should I use a third-party auditor or audit myself?

If you are spending more than a container on the first order, a third-party auditor pays for itself — they know which documents are commonly forged and will check them against official registers. For smaller trial orders, the checklist above plus a third-party pre-shipment inspection is usually enough.

Which certificates prove a battery factory is competent?

ISO 9001 for the quality system, plus product-level evidence: UN38.3 test summary, IEC 62133, and for the EU a CE declaration. Certificates alone prove very little about the pack you are buying, which is why the on-floor checks matter more than the certificate wall in the meeting room.

What should I do if the audit finds problems?

Separate the findings into things that can be fixed in weeks — record-keeping, test logs, labelling — and things that cannot, such as no grading capacity or no ageing area. Ask for a corrective action plan with dates, then verify it on the next visit or the next video audit.

Request an audit or a quotation

Send your drawing, target voltage and capacity, monthly volume and destination market, and we will answer with a buildable specification, a lead time and the export file for that configuration. Start on WhatsApp, or browse battery packs and electric two-wheelers to see what is already in production.