Old iPad 2, battery long since dead and won't hold a charge. Otherwise in good shape so I wanted to replace just the battery.
Getting the iPad open was the hardest part, I used a heat gun and ~130 degrees seemed to do the trick. My biggest issues was with the digitizer cable on the left side. I was not very careful, got ahead of the instructions and sliced the ribbon to, umm, ribbons. The rest of the repair was tedious but doable. When the glue is hard use heat as suggested. Replacing the battery and putting everything back was a breeze in comparison. I'm waiting for the new screen/digitizer to complete the repair, but that should be minor at this point.
Read the whole guide, follow each step, and don't use more pressure to get anything out or heat to get anything loose than needed.