After one year of service the battery of my iPhone 4S started to show signs of weakness. When I used the data connection or the GPS more than usual, the device often ran out of power before the end of the day. I worked around the issue by disabled I few things including the Bluetooth and even the Wi-Fi. My cellular plan includes enough data per month and the 3G network is fast enough in Paris that I could update apps and download podcasts painlessly via 3G.
However now my iPhone is 2-year old and once again the battery cannot last a whole day anymore. The issue is probably aggravated by the cold winter. Anyway this time I decided to actually do something about it. Apple charges 75 euros to replace an iPhone battery so I looked at the iFixit iPhone 4S battery replacement guide and it seemed reasonably easy and you can find an iPhone 4S battery on eBay for 5 euros, plastic tools included and free shipping! I don't expect to have an original, Apple-certified battery for that price but I decided to give it a chance anyway.
To have a rough idea of the state of my old battery, I did two things. First I charged it fully and then I played the Nyan Cat video in fullscreen mode using the Youtube app. I recommend muting the iPhone or you'll probably get crazy after about 5 minutes. The battery latest a little over 3h.
I also found a piece of software called iBackupBot that is able to extract some of the battery stats from the iPhone. It said that after 626 charge cycles, my battery full charge capacity is at 1024 mAh (compared to the original 1430 mAh).
As expected the iFixit guide is perfectly clear and detailed. The only thing that I found a little confusing was the ground clip mentioned at step 5. I was not able to avoid moving it so I was just very careful to put it back in the same position underneath the top screw when I put everything back together. Once I was done the iPhone booted with no issue and everything was working fine (3G, Wi-Fi etc.).
The new battery was only charged at 25% so I recharged it completely and then I did the same tests than before. The video playback lasted about 6 hours (twice as much!) and iBackupBot confirmed that the battery is back to its nominal capacity. Mission accomplished.
The least I could say is that I am very happy about the whole experience. The battery replacement took me maybe 15 minutes, it works like a charm and I saved something like 70 euros.
Important note: iPhone batteries are lithium-ion polymer (LiPo) batteries. These batteries are known for their good capacity to size/weight ratio but they are also known to explode or burst into flames if not properly managed. This is a risk you need to take into consideration. I decided to take the chance because I am cheap and because I like to fix things myself but you should do your own research on the subject before you decide if it is a chance you are willing take.
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