Apple has confirmed a battery meter bug that has been plaguing iPhone 6S and iPhone 6S Plus. When the bug is in action, it stops updating the battery percentage meter as per the actually remaining battery life. So a large number of users have had the misfortune of phone battery running out even when the meter says battery is full.
According to users and Apple, the bug is triggered if users change the time manually or if they take the phone to a different time zone. Apple says iOS 9.3 update which is currently in beta testing can fix this issue and they are trying for a permanent solution. Till then users are suggested use the automatic time settings of the phone.