iPhone 5S shuts off unexpectedly

[inbtw33n]

It's a 32GB iPhone 5S on iOS 10.2 10.3.1

This problem happened two times since last week. I've been on iOS 10.2 for months. I started to get these problems after the update. Not sure if the two are correlated. When I try to turn it on by holding the sleep button, nothing happens (no plug in usb charger icon, nothing; just black screen). I tried doing a hard reset by holding the home and sleep buttons together and that worked. I'm worried that this will be a big problem later on.

Does anybody else have experience with this or know what I should do to prevent bigger problems down the road?

PS. The problem I describe is not unlike the problem they describe on the Dec. 19, 2016 osxdaily article titled "iPhone 6s Unexpectedly Shuts Down? Apple Might Have a Fix!" But they don't really talk about the iPhone 5S there. Not sure if I'm allowed to post links so posted the title instead.

Edit: After hard resetting, 1st time the battery displayed ~75%, 2nd time the battery was ~82%.
Edit2: I was mistaken. The phone was recently updated to 10.3.1 from 10.2.

 

[44267547]

Perhaps it's your battery. At what percentage does your iPhone power off?

 

[inbtw33n]

Oh sorry, I forgot to add that both times it displayed >70% after the hard resets. I'll add the info in an edit.

 

[aKansasKid]

My wife's 16GB 5s did this three times yesterday, for the first time ever. It updated to 10.3 recently, for what it's worth, and I've heard no shutdown reports from her yet today. Battery was 89%. She's a minimalist user with minimalist apps.

 

[inbtw33n]

My wife's 16GB 5s did this three times yesterday, for the first time ever. It updated to 10.3 recently, for what it's worth, and I've heard no shutdown reports from her yet today. Battery was 89%. She's a minimalist user with minimalist apps.

Oh sorry I was mistaken. My wife told me she updated it to 10.3.1 last week. I thought she had stayed on 10.2. These problems started last weekend so there MIGHT be a correlation.

 

[brilliantthings]

Same thing happened to my wife's iPhone 5s while on iOS 10.3.3

Was shutting down multiple times per day. Had phone replaced under warranty with another 5s. Same thing kept on happening despite restoring to 11.2.1 in iTunes, not restoring from backup, replacing sim. Took to Apple store for the third time and they replaced with SE. In Australia our customer service laws are very protective, which explains the SE, but have met several people who have had exactly the same problem. There's something fishy with the 5s.