How do I fix this?
Here’s the quick summary. I’ll expand on this more below.
- Backup everything (ideally, an encrypted back up in iTunes)
- Put your phone into DFU mode
- Re-install iOS (as of writing, this is iOS 9.1)
- Restore your backup
WARNING: This means deleting everything off your phone and copying it back. If you don’t feel safe doing this, go to the Genius Bar at your local Apple store and ask for some real help instead of getting free advice off the internet.
Why does my iPhone shut down at 30% battery?
Short answer: I don’t know.
My theory is that the iPhone is confused about where 0% battery is and where 100% battery is. It thinks it has 30% left and then boom, out of juice. It thinks its fully charged when it really isn’t because it’s battery measuring is all off.
What causes this to happen? I can only speak anecdotally to this and I’m not an electrical engineer or anything. I went on a week long road trip that totally threw off my iPhone charging routine. During the day, it would be plugged into the USB port of the car and stuck at 100% for long hours. During the night, it would drain or charge off an external battery. It was also subjected to freezing temperatures while we camped out. All through this, we’d go in and out of really poor reception.
Detailed steps to fix it
You will need:
- Your Apple ID and password, memorized or written down
- Your iPhone that is hopefully in good working order
- A computer with enough hard drive space to store your phone backup
- A lightning cable
- Good wifi network for your newly-restored iPhone to download from
- Some spare time during which you don’t need your phone
Follow these steps to make an encrypted back up in iTunes. While it’s doing that, think long and hard about what things on your phone you would hate to lose and make sure to get a copy of them. For extra protection, do an iCloud backup as well.
Put your phone into DFU mode
Device Firmware Upgrade mode is a special mode on the phone that allows some low-level system software to be updated. I suggest restoring in this mode just to wipe the slate as clean as possible and clear out any inaccurate software assumptions about your iPhone battery.
To do this:
- Plug in your iPhone to your computer and have iTunes open
- Power off your iPhone (hold down the Power button and slide on the “power off” slider)
- Wait for it to be completely off
- Hold the Home and Power button for 10 seconds
- Keep holding the Home button but release the Power button
- Wait for iTunes to say that it’s detected a device
Don’t touch the phone, just follow the instructions in iTunes to restore the operating system.
Restore your backup
Soon you’ll see your iPhone load up the “Hello” screen. iTunes should prompt you to restore the backup you made earlier. Let iTunes do its thing and when it’s finally done, you can start using your phone. Check that all your settings are intact and hopefully your apps will all be downloaded shortly.
Everything should be fixed now! Use your phone as normal and you should be able to drain the phone to 0% battery again. If not, go to your local Genius Bar.
How do I prevent this from happening again?
Who knows? The future is unwritten. My suggestions:
- Don’t subject your phone to extreme temperatures
- Use only USB chargers, cables and batteries that are either directly from Apple or have the Made for iPhone logo (I prefer cables/batteries from Anker)
- Make regular backups