No one is using a little sticker hidden on your battery to spy on you, no matter what Facebook tells you.
It’s easy to get confused by the inside of a smartphone, even if you’re reasonably familiar with a lot of the technology that goes in to these devices. NFC chips are particularly curious, as their size makes it easy to sneak them in just about anywhere, and most folks outside of the tech bubble have no idea what NFC is or why we need the tech on our phones. In fact, all it would take to get someone worried about NFC is a reasonable-ish theory about government surveillance and a narrative that suggests the technology is being hidden from you somehow.
That’s exactly what is happening on Facebook right now, thanks to a video making the rounds detailing a “disturbing discovery” under a Samsung battery.