Add cookbook entry for battery levels

source/_cookbook/track_battery_level.markdown

@@ -0,0 +1,38 @@
+---
+layout: page
+title: "Track your battery level"
+description: "Basic example how to track the battery level of your mobile devices."
+date: 2016-01-29 09:00
+sidebar: false
+comments: false
+sharing: true
+footer: true
+---
+
+### {% linkable_title Battery level %}
+
+The [iCloud](/components/device_tracker.icloud/) is gathering various details about your device including the battery level. To display it in the Frontend use a [template sensor](/components/sensor.template/).
+
+```yaml
+  - platform: template
+    sensors:
+      battery_iphone:
+        unit_of_measurement: '%'
+        value_template: >-
+            {% raw %}{%- if states.device_tracker.iphone.attributes.battery %}
+                {{ states.device_tracker.iphone.attributes.battery }}
+            {% else %}
+                {{ states.sensor.battery_iphone.state }}
+            {%- endif %}{% endraw %}
+```
+
+While running the [Owntracks](/components/device_tracker.owntracks/) device tracker you can retrieve the battery level with a MQTT sensor.
+
+```yaml
+  - platform: mqtt
+    state_topic: "owntracks/tablet/tablet"
+    name: "Battery Tablet"
+    unit_of_measurement: "%"
+    value_template: {% raw %}'{{ value_json.batt }}'{% endraw %}
+```
+