My iPhone 6 was running slow, experiencing a lot of glitches and the battery drained quickly. Hoped a new battery would give the phone new life.
Most of the steps are pretty easy, but placing the battery with the adhesive is super important to get right and easy to place wrong. Because of this the repair took longer than it should have. The phone, however, is working again. Note, some of the glitches remain, which I think is due to the phone being older and Apple's inclination to ignore older phones with each new iOS update. So, hope to get another year out of my iPhone 6, but clearly will still need to replace it eventually.
iFixit instructions said to line up the battery with the top of its slot--WRONG. Doing so causes the battery connector to be a bit too high for the connection. Placing the battery according to those directions with adhesive applied necessitated the need to bend the connector into shape which didn't go very well. I did eventually make it work, but not without some cursing and wasted time. My advice is to place your battery by aligning the connectors instead, and to do so BEFORE you apply the adhesive just to see for yourself precisely where to position the battery for a quick, easy, correct fit. You'll save frustration and your phone will perform better after.