Li-ion Polymer Battery (Pouch Battery) this haves two swelling specification

[Kiriakos GR]

This article is relative Li-ion Polymer Battery (Pouch Battery) this used at tablet products, or at electrical T&M tools.
Most tablet products they have a low relative consumption, and or a know power consumption.

The proper designed charger, this will never misuse the battery at charging.
The known power consumption, this helped an engineer to select the proper battery for such a device.

Even so, the expert battery makers, they do deliver at product specifications, an expected swelling specification.

Example:
Cell Thickness max  / initial / 10mm
After 300 cycle life  / 10.8mm
This is an approximate of 8% of thickness change.
And this is expected at any cell capacity.   

At Li-ion Polymer Battery (Pouch Battery) manufacturing,  the cell becomes totally flat after the process of baking,  and there it also starts the first stage of battery capacity verification.
In conclusion, slight swelling this is inevitable, and or this is to be expected.

Extreme swelling, this is usually seen at poor quality power banks.
Most of times, the electronic controller this is designed for specific quality and capacity of cells, than the ones actually installed.
And or, electronic controller damage this will destroy any connected cells.
Golden advice, if a power bank this fails within it first year, never try to repair or replace the battery.