Today, we will look into what is the reason why your iPhone turn off at 30% (more ore less) battery life and what is the solution for this issue. There are many, many complains about the iPhone turning off and going completely dead, without the possibility of restarting the device, when there is still battery for about 30%. Some would say that this is a hardware issue, but let's see if indeed is it.
Out of the blue, many iPhone users have faulty batteries and that is causing the issue, but only for iPhone 5, 5s, 6, 6s, and 7. This is a very unlikely scenario yet still, there is a chance the some devices might have a battery issue but for sure not all of the reported cases, in fact most of them probably does not have any kind of problems with the battery.
Note: If your iPhone does not charge at all, there is a neat tutorial on Fix IT George! on how to fix that problem.
There is also the possibility that your iPhone is turning off without a warning due to a water damage and if you know your phone has taken a bath lately, the following solution might not work for you, however, you might wanna give it a try.
What might cause the problem?
In most of the cases, it's probably a firmware (Operating System - iOS) issue, perhaps a bug related to a software update, especially over Wi-Fi. Yes, even iOS can have bugs or package losses over a Wi-Fi update and this is why we always recommend updating your iPhone trough your computer using iTunes.
The idea is that the firmware might mistakenly communicate with your hardware, especially the battery in our case, and get incorrect information regarding the battery percentage. This might trigger a signal that the phone needs to be shut down and will not do anything until a charger is used. After plugging a charger users have reported that the phone starts charging from the percentage displayed when it was turned off.
1. Backup your iPhone
Before doing any type of actions related to the Operating System (iOS) you need to always backup your iPhone. I recommend you to do the backup on your computer using iTunes and for later simplicity, you should encrypt your backup so the passwords and all the sensitive data will be back in place once your restore your backup.
Should not be said, but use your iPhone with a connected iCloud account so your contacts, favorites and notes are safe in case you decide to set up your phone as a new iPhone (clean install). If you worry about the tons of pictures, check out here how to backup your photos and videos in the cloud for free.
2. Do a DFU restore
In order to start acting again normally, we need to restore the iPhone firmware, but not a regular restore / reset from your phone because this way you'll only delete the content but all the main components remains the same and, we want to restore a clean copy of iOS to have it's main components fixed. For this, we need to do a DFU (Device Firmware Update) restore using iTunes. We have made a tutorial on how to enter your iPhone in DFU mode if this is unclear for you.
After the restore is done you can recover your backup made earlier trough iTunes, however, it is recommended that you setup your phone as a new iPhone and install your Apps manually. Your contacts, favorites and notes should be recovered trough iCloud and your photos and videos trough Google Photos.
3. Do 100% charge / discharge cicles
Now that your iPhone is like brand new, it is recommended to have it charged to 100% and than let it fully drain out a few times. This way, your firmware will learn to get the correct information from your battery and you are doing a service to your battery as well.