Many features in your Nokia Lumia phone increase the demand on battery power and reduce the battery life time. For example if the signal strength of the mobile network varies much in your area, your phone must scan for the available network repeatedly. This increases the demand on battery power.
You can set your phone to automatically save power when the battery charge level is low. To check the battery status, and switch battery saver mode on, go to Settings > battery saver. Windows Phone 8: To choose when you want battery saver mode to be activated, switch Battery saver toggle to On and tap advanced.
Note: When Battery Saver is on, your phone will no longer: automatically receive email and calendar updates, update some Live Tiles and allow apps to run in the background.
If you are listening to music or otherwise using your phone, but do not want to make or receive calls, switch airplane (flight) mode on under the Settings menu.
To save battery power, note the following:
Use network connections selectively
Anything else I need to know?
The instructions to save power on your Lumia phone presented on this video (English) from Nokia Care.
If the battery drains faster even there is no active feature or applications, try to switch off the power and then switch back on. The battery may also be worn out and needs to be replacing with a new one.
The screen gets switched off during a phone call when the proximity sensor is covered. This is done to avoid accidental touch screen actions when you are in a call. To switch the screen on, hit the power (lock) key.
If the screen gets switched off immediately when dialing a number or receiving a call, check that the proximity sensor area at the upper front of the screen is not covered by any kind of protective film or tape.
You can take the following steps to check the issue. If the screen keeps switched off, the protector may not be of the right size and will block the sensor on the upper part of the front side. Then either remove the protector or cut off the plastic from the blocking area.
In case of audio issues, check the following: