blueprint tutorial

battery_low_mobile_notification.yaml

blueprint:
  name: Low battery level detection & notification for all battery sensors
  description: Regularly test all sensors with 'battery' device-class for crossing
    a certain battery level threshold and if so execute an action.
  domain: automation
  input:
    threshold:
      name: Battery warning level threshold
      description: Battery sensors below threshold are assumed to be low-battery.
      default: 20
      selector:
        number:
          min: 5.0
          max: 100.0
          unit_of_measurement: '%'
          mode: slider
          step: 5.0
    time:
      name: Time to test on
      description: Test is run at configured time
      default: '10:00:00'
      selector:
        time: {}
    day:
      name: Weekday to test on
      description: 'Test is run at configured time either everyday (0) or on a given
        weekday (1: Monday ... 7: Sunday)'
      default: 6
      selector:
        number:
          min: 0.0
          max: 7.0
          mode: slider
          step: 1.0
    notify_device:
      name: Device to notify
      description: Device needs to run the official Home Assistant app to receive notifications
      selector:
        device:
          integration: mobile_app
variables:
  day: !input 'day'
  threshold: !input 'threshold'
  counttotal: "{{ states.sensor \
| selectattr('attributes.device_class','eq','battery') \
| sort(attribute='state') | rejectattr('state', 'in', ['0', '100']) \
| list | count }}"
  countlow: "{{ states.sensor \
| selectattr('attributes.device_class','eq','battery') \
| sort(attribute='state') | rejectattr('state', 'in', ['0', '100']) \
| selectattr('state', 'lessthan', threshold|string) | list | count }}"
  listtextlow: "{% for batt in states.sensor \
| selectattr('attributes.device_class','eq','battery') \
| sort(attribute='state') \
| rejectattr('state', 'in', ['0', '100']) \
| selectattr('state', 'lessthan', threshold|string) \
| list -%}
{{ batt.attributes.entity_id }}
{{ batt.attributes.friendly_name }} is {{ batt.state }}% 

{% endfor %}"
  notification_message: "{% if countlow > 0 -%}{{countlow}} out of \
{{ counttotal }} device batteries are low:

{{listtextlow}}
{%- else -%}
All {{counttotal}} device batteries are ok!
{% endif %}"
trigger:
- platform: time
  at: !input 'time'
condition:
- condition: template
  value_template: '{{ sensors != '''' and (day | int == 0 or day | int == now().isoweekday())
    }}'
action:
- device_id: !input 'notify_device'
  domain: mobile_app
  type: notify
  title: 'Battery Check'
  message: '{{ notification_message }}'
- service: persistent_notification.create
  data:
    title: 'Battery Check'
    message: '{{ notification_message }}'
    notification_id: battery-check

For anyone else just finding this, I don't think it works any more. Devices all report as being fine even if they fall below the threshold you set.