XML set background (Android)

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/rootRL"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/battery"
    android:orientation="vertical" >

</RelativeLayout>