Before you replace anything reduce your screen brightness to a lower setting and close all of your apps that are not in use. Another possibility can be your cellular data usage. If you are always using cellular data your phone will die faster than usual. If this doesn’t seem to work there may be a problem with your battery. If so by a new replacement battery and refer to the Nokia Lumia 520 Troubleshooting to see how to replace it.
First check if the headphones are plugged in properly. If you continue to hear the static test your headphones with a different device. Finally if you still hear static there could be a problem with your audio jack. Refer to the Nokia Lumia 520 Troubleshooting to fix the problem.