iPhone 5s 16GB iOS11 randomly restarts I think it has to do with iOS 11.
I have tried updating to latest 11.2.1, but it did not help, also tried backup, reset, and restore did not help.
Does anyone have a solution?

EDIT 12/21:


I should mention that I took it the Apple store, and they did not find any issues. They recommended backup, erase and restore.
Also take a look as this user suggest the issue is iOS 11 - https://discussions.apple.com/thread/8101649
I downloaded app that show battery capacity status - it is 1400/1570mAh 89%, this means its not a battery issue.


EDIT 12/25:


Went again to apple store to ask to try replace battery and see if that help. They did full test again, and said it seem like software issue, all hardware is in great condition. And they recommended reset without restore. We did full reset and I did not install any apps, and the issue is still not resolved.


EDIT 1/18/2018:


I bought a new battery from iFixit. It did not resolve the issue. I did notice that switching to low battery mode does help reduce the random shutdowns, but not completely resolve it. I guess my solution is switch to android device.


I believe that if apple would allow switch back to iOS 10.3.3 , then that would probably have resolved it. I assumed the latest iOS would be better, but probably not for older models.
Your issue could be one of two things: the battery or an issue with your OS. 

You said you have already had your battery tested, but battery apps aren't very accurate and different tests at the Apple store will show different results. 

Start by calling (or chatting with) Apple support. Do this on a different device. Ask if they can remotely run a Mobile Resource Inspector test. This will test many different components in your phone and is how they diagnosed my battery issue.

If they determine it is not a battery issue, do a FULL restore. You'll need a computer with iTunes for this.


  As always, make sure all of your data is saved. You will not restore from a backup, so save it another way.


Start by putting your phone in recovery mode.


Shut down your iPhone.
Press and hold both the Home and Top buttons until the connect to iTunes screen appears.
Connect to iTunes.


iTunes will show a popup asking if you'd like to restore or update. You'd like to Restore.



Your computer will download a completely new copy of iOS 11 - that's what makes this different than doing this on an iPhone.

If your computer takes longer than 15 minutes to download the update, you'll need to put your phone in recovery mode again. Press and hold the Home and Top buttons at the same time to do this.


  Warning: Restoring your phone this way will require your Apple ID password unless you didn't have Find My iPhone enabled. If you do not remember your Apple ID password, you should reset it at iforgot.apple.com


If none of this fixed your phone, I'd recommend talking to Apple Support about your issue over the phone. (Over-the-phone support is generally faster than live chat)