They're lies, but the batteries work. There were Chinese lines manufacturing knockoff BL-5Js, and there may still be one or two, or just a bunch of crates filled with old ones. Source: still use an N900, but just for podcasts.

> 10-year-old if you count compatible Lumias

Worse, those Lumia BL-5Js aren't actually compatible. The slots cut into the battery aren't wide enough to fit into the N900. Unless you're willing to cut apart the battery itself, they're useless.