# Battery status

A device which can report its battery level can do so in two ways:

1. Report when the battery is empty or low.
2. Report the precise battery level that is left.

Give your driver the `measure_battery` capability if it supports reporting precise battery levels on a certain numeric scale (e.g. 0-100%). Give your driver the `alarm_battery` capability if it supports alarm notifications when the battery level reaches a certain threshold (e.g. 'battery level less than 10%).

> Never give your driver both the `measure_battery` and the `alarm_battery` capabilities. This creates duplicate UI components and Flow cards.

Battery devices must specify an energy object with the `batteries` property. This should be set to an array of strings which represent the batteries in the device. For example, a device with 2 AAA batteries must specify the following energy object:

{% code title="/drivers/\<driver\_id>/driver.compose.json" %}

```javascript
{
  "name": { "en": "My Driver" },
  "images": {
    "small": "/drivers/my_driver/assets/images/small.png",
    "large": "/drivers/my_driver/assets/images/large.png"
  },
  "class": "sensor",
  "capabilities": ["measure_battery"],
  "energy": {
    "batteries": ["AAA", "AAA"]
  }
}
```

{% endcode %}

For more information check the [Energy documentation](https://apps.developer.homey.app/the-basics/devices/energy).