How to completely turn off the XV6800 phone?

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Does anyone know how to completely turn off the XV6800 to conserve battery power?
I know WiFi is a big consumer of battery power, therefore, I always leave it off until I need to use it. I do camping a lot and there is no power outlet at camp site for recharging. In attempt to conserve battery, I switch the device to flight mode. That is supposed to turn off both the phone and the data. But my phone is still loosing battery power. I don't know what is causing it. So can anyone tell me how to completely turn the phone off and not to loose battery power?
Any help will be very much appreciated.