Last night, not having a means to charge an IPhone 6s I turned it off. The battery level indicator at that point said the remaining charge was 21%. Restarting the phone in the morning, the battery level indicator said 11%. Does turning off and starting it several hours later normally require 10% of battery?
EDIT: the phone was completely powered off. Hold down the right-side button and slide to power off. It was in that state for at 10 hours. I wouldn't expect any power usage in such a state.