I have the GPD Win 1 (Windows only) and while it's a pretty good pocket computer, I'm reluctant to ever buy another product from them because the support is lacking at best.
Several users have had batteries swell, and GPD has not provided any avenue for these users to get replacements. Some members of the community have stepped up, but the batteries are subject to shipping rules, so people in some countries are still out of luck.
No. Without getting into too much detail (the /r/gpdwin subreddit can provide more info), the battery has to be a specific voltage, high drain and a specific size because the chassis has very little room in it. There are knockoffs of the battery on AliExpress, but people who have bought them have reported having all sorts of problem with them.
The unit also won't work without a battery on AC power only, because it looks like it was made with pre-existing tablet guts in that it only gets power from the battery irrespective of whether it's charging or not.
And given that the OEM batteries are subject to expansion, there's no reason to think that an OEM replacements wouldn't either.
FWIW, the GPD Win 2 doesn't have these issues, because it has a different design.
Several users have had batteries swell, and GPD has not provided any avenue for these users to get replacements. Some members of the community have stepped up, but the batteries are subject to shipping rules, so people in some countries are still out of luck.