My battery had started swelling so I decided to replace it. It turned out to be a very simple procedure. Thanks iFixit!
Replacing a swollen iPhone 4 battery
I managed to replace the cracked digitizer panel on my iPad 3, but ended up with an overly sensitive home button which constantly triggers Siri on its own. So esthetically it was a success but from a functionality standpoint the device worked better before the repair ¯\_(ツ)_/¯