Battery readout on iPhone 5

If you are running IOS 10 this is a common problem especially on the newer phones. Even if you are not running IOS 10 you can still give this a shot. I have done this little trick multiple times on my own phones and it has saved me a battery change more than once. What you are going to do is a forced restart, (this also works if your phone freezes for any reason). Hold down the power and home button at the same time until the screen goes black then let go of both. Restart the phone with the power button and it should take care of your problem. If it continues, do the same process except this time leave the phone off and charge it for about 4 hours on your wall charger with an Apple certified cable and wall block. Using non Apple certified chargers can internally damage your phone. Note: If the phone turns on when you plug it into the wall there is an internal problem with your power management chip, if that is the case I would use the phone for as long as you can and upgrade. You can change the battery but it will eventually return but that may buy some time.

Here is an answer I had previously found when I had the problem on Apple Discussions, no credit to myself.

"What you need to do given your current problem: When the phone shuts off and it isn't down around 1%, connect to a charger for just a minute or 2, or wait 15 minutes, then reboot the phone (hold HOME and SLEEP until an Apple logo appears). Continue running the battery down until it shuts off around 1%. If it goes off above that value repeat the above process until you really do get to 1% (this will rarely take more than 2 tries).

Once it has turned off and won't restart or reboot charge it with the wall charger for 4 hours without using the phone. This should fix the problem for the moment. Going forward, about once a month run the battery all the way down and charge for 4 hours. This should prevent the problem from recurring."