A swollen power bank is a safety event, not a cosmetic complaint. The cell has generated gas, the enclosure has deformed, and the mechanical protection around the cell is no longer what it was when the product was tested.

That changes how the case should be handled at every step: by the user, by the retailer taking the return, and by the brand processing the claim.

Why does a power bank battery swell?

Gas builds up inside the cell.

Overcharging, sustained heat, internal short circuits, mechanical damage and normal ageing can all cause electrolyte decomposition and gas generation inside a lithium cell.

A lithium-ion cell contains an electrolyte that can decompose when the cell is stressed. The decomposition produces gas, and because the cell is sealed, the pressure has to go somewhere: the pouch or the cylindrical can deforms, and the product’s enclosure visibly swells.

The stress that triggers it is usually cumulative rather than a single event. Charging at elevated temperature, leaving a device on charge in a hot car, and cycling a cell to the end of its life all leave the cell closer to that threshold. A physical impact that dents a pouch cell can start the process immediately.

What should you do with a swollen power bank?

Stop using and stop charging the unit. Move it away from anything combustible and out of the sun, and do not attempt to open the enclosure or press the deformed surface back into shape. A swollen cell is mechanically fragile, and puncturing it can turn a swelling event into a fire.

Disposal should follow the rules for lithium batteries rather than general waste; the US Environmental Protection Agency publishes guidance for used lithium-ion batteries (US EPA: Used Lithium-Ion Batteries), and air transport of lithium cells is regulated separately by the FAA (FAA PackSafe: Lithium Batteries). In the EU, battery-specific obligations apply across the product’s life cycle (Regulation (EU) 2023/1542). Where a product has swelled, the safe handling instructions matter more than the refund conversation, and support documentation should lead with them.

Is a swollen battery covered by a warranty?

It is covered when the swelling is caused by a defect in materials or workmanship, and that is what a claim assessment has to establish. WECENT’s power banks carry a standard two-year warranty, and claims are handled through a structured after-sales process that includes batch traceability, which is what allows a brand to trace a returned unit back to its production batch and test record.

The assessment is the same one used for other defects: record the unit, inspect the enclosure and the charge history where available, check the batch record, and decide between replacement, credit and failure analysis. What changes with a swelling case is the urgency, because the unit should not sit in a returns cage for weeks.

Delivery and packaging requirements

Lithium cells move under transport rules that restrict how batteries may be shipped and declared, and a swollen unit is not in the condition the original packaging was designed for. Returns procedures should specify a fire-resistant container or pouch where local rules require one, and should avoid compressing the unit in a standard envelope.

For brands, the same consideration affects the outbound side: enclosure design and transit testing determine whether a cell arrives undamaged in the first place. The ISTA protocol family provides published test sequences for parcel distribution that a supplier and a brand can agree on (ISTA).

Design factors that reduce swelling risk

Four design decisions carry most of the risk reduction. First, cell qualification: sourcing cells from a supplier with traceable process control and inspecting incoming material for physical damage. Second, charge management: a protection IC and firmware that hold the cell inside its voltage and temperature limits. Third, thermal behaviour: spreading heat away from the cell and derating charging when the temperature rises. Fourth, enclosure engineering: enough rigidity that a normal drop does not deform the cell.

WECENT’s quality control gates include incoming material verification, ESD-controlled PCBA processes, 100% functional testing, hi-pot pressure testing and load aging, with per-batch inspection reports. Those steps address the internal-short and manufacturing-defect triggers, which are the ones a factory can control most directly. The charging input side is a separate specification: the adapter used to charge a power bank is an external power supply with its own efficiency and documentation obligations in the EU (Regulation (EU) 2019/1782) and the United States (10 CFR Part 430).

Test protocols that catch cell problems before shipping

A practical production test programme combines four measurements: capacity verification against the rated value, internal resistance screening, charge and discharge behaviour at the cell’s limits, and a visual and dimensional check after load aging. Units that fail are removed before they reach the enclosure stage, where the failure would be far more expensive.

The record matters as much as the test. A batch record that links a serial number or batch code to those measurements is what allows a brand to answer a customer complaint with evidence rather than a replacement. In a swelling case, that record is also the fastest way to determine whether a single unit or a batch is affected.

How retailers and distributors should handle a swollen unit

Front-line staff need a short script: do not test it on a charger, do not open it, store it away from combustible material, and start the claim immediately. Photographs of the unit and the model label are enough for the first stage of most claims and avoid unnecessary handling. The input standard behind the product’s charging behaviour is USB Power Delivery (USB-IF: USB Power Delivery).

At programme level, spare parts, credit terms and the RMA flow belong in the same document as the warranty terms, which is how WECENT structures after-sales support for its OEM/ODM programmes and battery products such as the Qi2 magnetic power bank platform.

At the brand level, the process should define who pays return freight for a swelling case, what evidence is required, and how quickly a replacement is issued. Because the health and safety dimension is part of the complaint, speed is a material part of the response, and a distributor programme that covers spares and RMA flow for charger lines is the right place to document it.

Battery safety requirements vary by market and by product class. Verify the applicable transport, labelling and disposal rules for each destination before publishing a claim.