Please note that this only applies to smart phones with a removable back and battery.
Some phones, such as the iPhone and Nexus 5, do not allow you to remove the battery.
Please perform a power cycle by following the instructions below:
1. Power the phone off and remove the battery for 10-15 minutes.
2. Press and hold the 'Power/On' button for 5-10 seconds.
Following this, please reinsert the battery and power the device back on.
This will complete the power cycle procedure.