Portable Power Bank (OEM, 10,000–30,000 mAh)

Cell Quality: A-Grade vs. B-Grade

The single most impactful quality variable in a power bank is the cell grade. Factories buy cells from multiple tiers:

A-grade cells (Panasonic, Samsung SDI, LG MH1, CATL, EVE, LISHEN Grade A) meet the cell maker’s full specification for capacity, cycle life, and internal resistance. They carry individual traceability.

B-grade cells are production rejects or off-spec cells sold in bulk. A factory listing “18650 2,600 mAh” cells may ship B-grade cells with actual usable capacity of 1,800–2,100 mAh and degraded cycle life (often <200 cycles before hitting 80% capacity threshold).

How to verify:

• Request cell brand and model number in writing, include it in the purchase order
• Run a discharge test at 0.2C rate to 3.0V cutoff for each sample unit — compare the watt-hours measured against the rated capacity
• A 10,000 mAh / 3.7V nominal bank = 37 Wh rated. Acceptable measured discharge: ≥33.3 Wh (90% of rated). Below 30 Wh = suspect cells.

UN 38.3 Certification for Air Freight

UN 38.3 is the UN transport standard for lithium batteries and cells. Without a valid UN 38.3 test report, lithium battery products cannot be shipped by air (neither courier nor cargo). This is not a product certification — it is a transport compliance requirement.

Key points:

• UN 38.3 tests are performed at cell level and at battery pack level. Both are required.
• The test report must name the specific cell model. If the factory changes cell supplier, a new test is required.
• IATA Dangerous Goods Regulations (DGR) require the UN 38.3 summary test report to be available for inspection at shipment. Confirm the factory provides this document with each shipment.

For ocean freight, UN 38.3 is still required by most carriers under IMDG Code. Do not assume sea freight exempts you from this requirement.

Real Capacity vs. Rated Capacity

Chinese regulatory standards (GB/T 35590) permit capacity labeling based on the cell nominal specification, not measured output. This means a power bank with a rated capacity of 20,000 mAh may deliver only 10,000–12,000 mAh of usable charge to a phone — due to cell-to-output conversion losses (typically 80–85% efficiency), but also due to overstatement of cell capacity.

For export products, align with the EC Declaration of Conformity requirement: the labeled capacity should reflect actual output capacity (Wh), not cell nominal capacity in mAh. Some EU market retailers require a Wh rating on the label instead of mAh.

Common Pitfalls

PD protocol compatibility. A bank supporting “USB-C PD 45W output” must implement the full USB PD 3.0 power negotiation stack. Devices that charge only at 5V from a USB-C port (not PD-compatible) will not trigger fast charging from a non-PD-capable bank. Test with the actual end-user device before finalizing the design.

21700 cell lead time volatility. 21700 cells have tighter supply during EV battery demand peaks. Confirm cell availability for your production window at least 60 days in advance.