How much battery percentage is used depends on what you are using. I'm guessing that you are referring to how much charge is being used from the 100% you started with at the beginning of the day. Certain apps and processes use more battery depending on the amount of processor needed. Graphics intense tasks use more battery. If you are using cellular data, the strength of your signal will also affect the amount of power used to maintain a connection. You can go to Settings>Battery and look at the graph on the page and scroll down and it will display the amount of battery usage by app and that can help you determine what is using your battery. If the battery is using large amounts while just sitting there not doing anything, then you may need to investigate what app or apps are using battery during that time.