MagSafe battery?

It is a battery pack that supplies additional battery capacity: MagSafe Battery Pack - Apple

also see the following from that link:

Attaching the MagSafe Battery Pack is a snap. Its compact, intuitive design makes on-the-go charging easy. The perfectly aligned magnets keep it attached to your iPhone 12 or iPhone 12 Pro — providing safe and reliable wireless charging. And it automatically charges, so there’s no need to turn it on or off. There’s no interference with your credit cards or key fobs either.

At your desk and need a charge? Just plug a Lightning cable into the MagSafe Battery Pack for up to 15W of wireless charging. Short on time? With a higher than 20W power adapter, you can charge both the MagSafe Battery Pack and your iPhone even faster. And you can track the status of your charge on the Lock Screen.

MagSafe Battery Pack is a wireless charging battery pack that attaches to the back of iPhone 12 models. The battery pack was just released and iOS version 14.7 allows the recognition of this battery pack when it is attached to the iPhone 12. Click here ➔ to learn more about the MagSafe Battery Pack.

Axel F.