Keep latest value read from ble_client

Configuration
1

Hi,
I am trying to readout once a day the battery level of a BLE tag I am using for presence detection.
To read out the value I connect the ble client once a day. I would like to keep the battery percentage visible in HA. Now the sensor always becomes unavailable.

Is there any way to prevent ESPhome to send the unavailable flag?

My used code:

esphome:
  name: garage
  friendly_name: Garage

esp32:
  variant: esp32c3
  framework:
    type: arduino

esp32_ble_tracker:
  id: ble_tracker
  scan_parameters:
    continuous: false

# Enable logging
logger:

# Enable Home Assistant API
api:
  encryption:
    key: "**********"

ota:
  - platform: esphome
    password: "********"

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Garage Fallback Hotspot"
    password: "*********"

  on_connect:
    - esp32_ble_tracker.start_scan:
        continuous: true
  on_disconnect:
    - esp32_ble_tracker.stop_scan:

captive_portal:
ble_client:
  - mac_address: "00:00:00:00:00:00"
    id: AutoTracker 
    auto_connect: False
    on_connect:
      then:
        - delay: 1ms
        - lambda: |-
            id(BatteryLevel).update();

binary_sensor:
  - platform: ble_presence
    mac_address: 00:00:00:00:00:00
    name: "Auto Tracker"
    min_rssi: -80dB
    timeout: 
      seconds: 60

sensor:
 
  - platform: ble_client
    id: BatteryLevel
    ble_client_id: AutoTracker
    type: characteristic
    update_interval: never
    notify: False
    name: "Autotracker Battery Level"
    service_uuid: '180f'
    characteristic_uuid: '2a19'
    unit_of_measurement: "%"
    device_class: battery

time:
  - platform: sntp
    on_time: 
      seconds: 0
      minutes: 0
	  hours: 0
      then: 
        - ble_client.connect: AutoTracker
        - delay: 10 seconds
        - ble_client.disconnect: AutoTracker`Preformatted text`
2

I think the approach would be to use a Template Sensor with return {}; when BatterLevel is unavailable.

3

Are you sure that MAC address is valid? min_rssi?

4

Yes, the presence part works, and once a day it shows the battery level for a short time