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--I'd love to hear any suggestions (just be gentle, please).

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

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
    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 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.)

Monitored conditions

You can specify only those conditions that you'd like to track. The default is to track alarm, capacity, capacity_level, present, status, and 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 format: alarm,capacity,capacity_level,present,status,voltage_now

Example Home Assistant configuration

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