title: Checking battery level in the background with a service
body: <p>I've searched a lot but I'm always more confused.</p>
  
  <p>I have to create an app that works on background and checks the battery level. How can I create the Service? The Service should start on the device boot and must communicate with the Activity when the battery reaches a certain percentage, so there isn't any interaction from the consumer.</p>
  
  <p>What type of Service have I to create? What are the things I have to do?</p>