There are pictures online. And for an unexplainable reason it is the person behind the biggest Bitcoin exchange SNAFU of all times (where hackers stole something like 800 000 Bitcoins), Mark Karpeles of "Mt. Gox" (who did jail time btw), who was the first to post them:

Apparently the hacker did remove the battery and replace it with a smaller one, leaving enough room for the tiny eSIM/LTE modem / OCR chip that did recognition of the secret on screen.