Quick answer
Audit the cell source, the BMS design, the end-of-line test records and the certification file. Those four items predict field failure better than factory floor size. A supplier that can show cell batch traceability and per-unit test data is usually a safer partner than one that only shows certificates covering a different model.
IMG1. Cell sourcing and traceability
Ask which cell manufacturer is used, whether cells are A-grade or downgraded, and how a finished pack can be traced back to a cell batch. Reputable suppliers keep incoming inspection records including capacity, internal resistance and voltage. Request the last three months of incoming inspection data and check whether rejects are documented.
2. BMS architecture
- Does it monitor per-cell or per-module voltage? Per-cell is preferred above 100 Ah modules.
- Are overvoltage, undervoltage, overcurrent and temperature protections independent of firmware?
- Is there a hardware disconnect path, or does everything depend on the microcontroller?
- What communication protocols are supported — CAN, RS485, Modbus — and can the register map be shared?
3. End-of-line testing
| Test | What it catches | Evidence to request |
|---|---|---|
| Capacity test | Underperforming modules | Per-unit discharge curve |
| Insulation resistance | Assembly defects | Recorded value per unit |
| High-voltage test | Creepage and clearance faults | Test voltage and result |
| Aging / burn-in | Early cell failures | Duration and pass criteria |
| Communication test | Inverter compatibility issues | Tested inverter model list |
4. Certification file
Verify that the certificate names the exact model, the cell chemistry and the enclosure you are buying. Check the issuing laboratory and the certificate number independently. UL 1973, IEC 62619 and UN 38.3 are the baseline; UL 9540A matters for indoor installation in North America.
5. Production capacity and consistency
Ask how many packs per day the line produces at your specification, and what the changeover process is between models. A supplier running many small batches has more opportunity for assembly error than one running a stable configuration. Request the process control plan and the torque specifications for busbar connections.
6. Commercial terms that protect the importer
- Warranty stated in years and cycles, with a defined capacity retention threshold.
- Spare module availability commitment for the full warranty term.
- Written RMA process with response times and who pays freight.
- Firmware update policy and access to the register map.
- Serial number scheme that supports field traceability.
Bottom line
A factory audit is a document review exercise as much as a site visit. Ask for the data behind the claim — cell batches, per-unit test records, register maps, certificate scope — and the answers will separate assemblers from manufacturers.