I thought of this project when I switched to using my old laptop as my Home Assistant server. I wanted to track its battery level in Home Assistant to use in automations. I'm very new to Python, so I'm sure there's room for improvement here.

Summary

battery2mqtt can monitor current battery percentage, charging status, etc. for any batteries present at /sys/class/power_supply. The MQTT topic format is battery2mqtt/$TOPIC/$NAME where $TOPIC is the topic you define and $NAME is the name of each battery. For example, if /sys/class/power_supply/BAT0 is present in your system and you choose server to be the topic, the full topic will be battery2mqtt/server/BAT0.

Instructions

Option 1: Pull from Docker Hub docker pull tediore/battery2mqtt:latest (https://hub.docker.com/r/tediore/battery2mqtt)

Option 2: Manual build

Clone repo: git clone https://github.com/Tediore/battery2mqtt
Enter directory: cd battery2mqtt
Build image: docker build . -t battery2mqtt
Customize docker-compose.yaml to fit your needs
docker-compose up -d

Example compose file with all possible environmental variables listed:

version: '3'
services:
  battery2mqtt:
    container_name: battery2mqtt
    image: battery2mqtt:latest
    environment:
    - MQTT_HOST=10.0.0.2
    - MQTT_PORT=1883
    - MQTT_USER=user
    - MQTT_PASSWORD=password
    - MQTT_TOPIC=server
    - MQTT_QOS=1
    - INTERVAL=60
    - MONITORED_CONDITIONS=status,capacity
    - BATTERY_HEALTH=1
    - TIME_REMAINING=1
    - SHOW_UNITS=1
    volumes:
    - /sys/class/power_supply:/sys/class/power_supply:ro
    restart: unless-stopped

Configuration

Variable	Default	Description
`MQTT_HOST`	`None`	IP address or hostname of the MQTT broker to connect to.
`MQTT_PORT`	`1883`	The port the MQTT broker is bound to.
`MQTT_USER`	`None`	The user to send to the MQTT broker.
`MQTT_PASSWORD`	`None`	The password to send to the MQTT broker.
`MQTT_TOPIC`	`server`	The topic prefix to send the payload to.
`MQTT_QOS`	`1`	The MQTT QoS level.
`INTERVAL`	`60`	How often (in seconds) battery2mqtt polls for battery info.
`MONITORED_CONDITIONS`	(See below)	Battery properties to send to MQTT (must be a comma-separated string).
`BATTERY_HEALTH`	`1`	Set to 1 to enable battery health percentage calculation or 0 to disable.
`TIME_REMAINING`	`1`	Set to 1 to enable time remaining estimate (in hours) or 0 to disable.
`SHOW_UNITS`	`1`	Set to 1 to show power units in the MQTT payload or 0 to disable.

Monitored conditions

You can specify only those conditions that you'd like to track. The default is to track status, capacity, energy_now, energy_full, energy_full_design, power_now, voltage_now. You can add more conditions (found at /sys/class/power_supply/$NAME) or choose only those you want to track. The variable in your docker-compose.yaml must follow this comma-separated format:

status,capacity,energy_now,energy_full,energy_full_design,power_now,voltage_now

A summary of these conditions is below.

Condition	Description	Unit
Status	Battery status (charging, discharging, full)	None
Capacity	Current battery percentage	%
Energy now	Current battery capacity	Wh (watt-hours)
Energy full	Battery capacity when full	Wh
Energy full design	Original battery capacity when full*	Wh
Power now	Current power consumption	W
Voltage now	Current battery voltage	V
Battery health	(See next section)	%
Time remaining	(See next section)	Hr

Batteries lose capacity with each charge cycle. Energy full shows the actual full capacity of the battery due to wear; Energy full design shows the capacity the battery was able to hold when factory fresh.

Battery health and time remaining calculations

The default is to also provide a battery health percentage calculation by dividing energy_full by energy_full_design. This can be disabled by setting BATTERY_HEALTH to 0 in your docker-compose.yaml. Similiarly, an estimate of time remaining on battery (in hours) is calculated by dividing energy_now by power_now. This can be disabled by setting TIME_REMAINING to 0 in your docker-compose.yaml.

Example Home Assistant configuration

sensor:
- platform: mqtt
  name: Server battery
  state_topic: &server_battery_topic "battery2mqtt/server/BAT0"
  value_template: "{{ value_json.capacity }}"
  unit_of_measurement: '%'
  icon: 'mdi:battery'
  json_attributes_topic: *server_battery_topic