30 minuten - 1 uur
My battery was draining 1% less than every 2 minutes or so even when on power saver! Upgrading to iOS 9.0 caused something funny to happen to my battery, draining it from 100% to 0 in less than two hours and the result stuck on, leaving me with an under-performing battery.
When I was trying to remove the screen from the case, I accidentally pried apart the digitizer from the rest of the screen, so that got me really panicky. Luckily I used some tweezers to help lift off the bottom portion of the screen. It carried on smoothly afterwards until having to remove the adhesive strips from the battery. The adhesive strips weren't cooperating and tore apart as soon as I tried to remove them as instructed in the guide. That resulted me in trying to use the spudger stick to "un-stick" the battery by ramming it below the battery, slowly and cautiously. I was breaking apart in a nervous sweat because the battery started to bend and deform slightly, making me fear that it might catch fire all a sudden. I did not have any fire protocol safety system in case it did happen. After a grueling 20-30 minutes of ramming the stick like a crowbar to pry the battery off, it finally happened. Inserting the new battery and putting everything else back in after that was a piece of cake.
Some steps might go wrong but you can do it!