Pacemakers at least should be a non-issue since the law specifically exempts devices where continuous power is required for the safety of the user. I think an unpowered pacemaker would definitely jeopardize ones safety. But yeah my mind also immediately went to very small devices like hearing aids.

Maybe this is why Apple is focusing so much on health sensors. It's a bit of a stretch but it could be argued that Apple's fall detection and heart rate monitoring is required for the safety of the user.

Hearing aids already have replaceable batteries, don't they? I guess I don't know the whole market, but you can buy batteries for my brother's heading aids at Walmart. They take a minute or less to replace. Same with my friend's hearing aids.

Hearing aids have long had tiny, replaceable batteries - rechargeable hearing aids are an innovation, by comparison!

rechargeable hearing aids are pretty common place now, although they still gouge you a few hundred dollars for the convenience.