IOS 10 Battery life issues

Since the update to IOS 10 my battery percentage meter has stayed on 100% at all times. the only time is changes is if im using the phone to play a game or something and it all of a sudden just shuts off like its dead. i plug it into a charger and it comes back on almost immediately and says my battery life is some sort of percent 100, 40, 73, etc.. i have done a restore and it seems it will continue with the same issue. I have followed all the steps to save battery life and problem still happens. please help