I read it differently:
Further documentation stated "a portable battery shall be considered readily removable by the end-user where it can be removed from a product with the use of commercially available tools, without requiring the use of specialised tools, unless provided free of charge with the product".
I take specialized tool to mean for example, a screw than you can’t find a driver for at a hardware store. Since all you need to replace the battery are some Phillips heads and a blow dryer or heat gun, it seems fully possible for a consumer to replace the battery using commercially available tools. Difficult sure, but should comply as-is.
Steam deck already supports this