Do you turn your phone off when you drive your the car or go about your daily business? Unlikely.
If you leave your battery in your phone, even in the 'off' position, your phone is still on, still capable of receiving and sending, including E911. Just because the screen says it's been turned off, doesn't mean it's been turned off. Pull the battery out.
Soon though, that won't be enough, and your phone and other devices will be able to transmit their location, data, etc. without the need for a battery.