I use my old iPhone 4s for my extensive iTunes library and it had stopped charging. After trying every fix I could find online, I knew the battery had died (it was 9 years old). I received my iFixit replacement battery and tool kit within two days of ordering! I watched the guide video a few times so I knew what to do. The hardest part was getting the screws back in as I have little to no closeup vision and had to rely on my reading glasses. But it worked and the phone is now charged 100%! The replacement task was a bit stressful, but for $16+ I have no complaints! Thank you, iFixit!