While the phone is still warm/hot (and don't burn your hands), insert a guitar pick/opening tool underneath the battery around the top. some force will be needed

If all is going well, you will hear the sound of adhesive releasing and your opening device will slide further underneath

If you've made it this far underneath the battery, the temperature has likely cooled down significantly. So, keeping the opening tool inside, you'll be heating the battery again. This may deform your opening tool if it is made of plastic, so use your least-favorite one