Pinebook Pro?

[chithanh]

1- use a rather standard battery

1 - There is no such thing as a standard battery

I think the 18650 cell is the closest to a standard battery there is.

The other cells are way too small, or are really bare cells which you can't expect the buyer to fit themselves. Handling bare lipo cells can be dangerous for users who don't know what they're doing, so you would need a case where + and - can't be switched.

You can buy bare USB portable chargers that you have to install 18650 cells yourself. I don't see why it is impossible for notebooks. But I agree that it is not for the average user, and careful handling is needed. And of course there is a problem in case of warranty claims, or if the notebook catches on fire...

Given the dimensions of the Pinebook Pro, it is physically too thin to provide a swappable battery

That the Pinebook Pro is too thin for that sort of thing is probably true.  I have seen some older netbooks that use batteries which contain 18650 or comparable cells, mounted between the hinges of the display (e.g. IdeaPad S12).