Seems pretty clear cut to me.
Now pretend you are Apple. They’ll see this legislation and think - “we want people to buy new phones, not keep what they have, so we need to fuck with users to make that happen”. So maybe they’ll define battery to include battery management system. Maybe even some DRM and some proprietary or encrypted device communication in between the battery and the phone. Now it’s hard for anyone to use their phone with an OEM battery because of the DRM. Or if they do permit OEM batteries then Apple could be dicks and put scary popups on the screen like they do when people replace their screens and gimp the battery so they can’t charge or discharge as fast .
And Apple could go further. If they’re the only ones selling ungimped batteries, they can control the price of those batteries and sell them sky high. $150 sounds like a great fuckoff price point to deter people. And who’s to say how many batteries they hold in stock - just because the phone has replaceable batteries doesn’t mean Apple sells batteries.
So that’s what you have to worry about. EU legislation does have some wording controlling spare part availability and prohibiting software restrictions on batteries so I would hope that is sufficient, but who knows.