Looks like the battery is glued down with heat sensitive glue. Those are the terminals to connect to a built-in heater (i.e. piece of wire). This replaces a finicky 3m-command-strip-like thing. That's what I gather; I've never opened a modern iPhone.

The glue isn’t heat sensitive- there is no built-in heater. The glue is chemically changed by the electric current to no longer adhere.