My iPhone SE on iOS 12 has been acting strange recently.

Yesterday, it turned off at around 10% and when I tried to turn it on it said that it has no power. Two minutes later, it turned on and said it had 14% capacity remaining.

Today, when it was at around 10%, it turned off. Then I turned it on and it said 12%. Two minutes later, it turned off. It says "connect to power."

After a few minutes I tried again and it turned on. Then it gives an error saying that it "can’t connect to my mobile data network" and then the phone crashes.

I turned it on again, and it worked normally.

What is causing this?

EDIT: After digging around my batter settings I found this:


  • So is the Performance management doing its job now ?
    – Ruskes
    Commented Dec 17, 2018 at 16:46
  • Since battery problems vary by model, would anyone mind if I put the model name into the title.
    – benc
    Commented Dec 17, 2018 at 17:20

2 Answers 2


Your battery is failing/has failed.

The symptoms that your iPhone is exhibiting is the same as what discussed in the following posts:

Basically, when you see a percentage of battery remaining, it's a calculation based on what it's measuring (volts, amps, draw, etc.) at that moment in time. You cannot measure remaining capacity - this especially noticeable if one of the in-line cells is faulty.

The only solution to this problem is to replace the battery.

  • 1
    On one of my other posts it was concluded that my batter was healthy. It’s health is at 94%. Will this be a persistent issue? Can I just keep my phone charged and it will be fine?
    – user310476
    Commented Dec 17, 2018 at 16:12
  • 1
    In your other question you didn't indicate you were having any issues. If you were to disclose the symptoms presented here in that previous question, you would get a vastly different answer. Just because it's got a low cycle count, and calculates a 94% capacity doesn't actually mean it's a 94% capacity.
    – Allan
    Commented Dec 17, 2018 at 16:18
  • I only had the symptoms from yesterday. So you recommend a battery replacement? I am kind of hesitant as it’s only been a year. What do you mean by “doesn’t actually mean a 94% capacity”
    – user310476
    Commented Dec 17, 2018 at 16:20
  • Also I edited my post with a new discovery
    – user310476
    Commented Dec 17, 2018 at 16:22
  • 1
    A 94% capacity is a calculated value based on measurements of the whole (all cells) at a particular point in time. It has no idea the condition of the individual cells and if one is failing there's no sensor in the iPhone that will tell you this. It's like putting a brick in your gas tank - you think it's full when it really only has 90% capacity and the car has no way of knowing the brick is in there.
    – Allan
    Commented Dec 17, 2018 at 16:25

nice answer Allan .

also please tell us how old your phone is.

I suggest going to settings-> battery-> battery health and see what does the number say. it can be a temporary fix if you can negotiate on either performance(will be fast but may shutdown) or experience(will be slow but won't go off).

Apple's letter regarding batteries

  • My phone is over a year old and the health is 94 %
    – user310476
    Commented Dec 17, 2018 at 16:13
  • @DaniilManokhin support.apple.com/en-in/HT208387 according to this article, several messages indicate diff. battery situations. and yours falls under normal degradation where no battery replacement is required. all you said was a combined effect of low battery and a sudden load after switch on. even I have the same situation as your phone. One day it crashed moments after turning it on and battery went from 60 to 9 and it heated up. after restart, I locked it and put it on airplane mode to relieve some pressure from network. and charged it ofc.it works fine. relax and wait till 80 %
    – anki
    Commented Dec 17, 2018 at 17:40
  • try not to let it go beyond 15 and use low power mode and turn off non essential services at that time. one more point I concluded after referring to many sites is that most shutdowns happen at the time of launching any app. I recommend not closing lighter apps. low power mode anyway disables Background refresh so charge decay is lower than constantly opening and closing. this may light up some debate here but it's an estimate and needs to be researched.
    – anki
    Commented Dec 17, 2018 at 17:45

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