Tired of plugging/unplugging my mac to preserve the battery. I wanted to use my home automation system. batt2mqtt simply sends the battery status to an MQTT server. With Node-Red, my home automation system can automatically turn the plug on/off when it's time.

According to Battery University, the battery lasts longest when operating between 30 and 80 percent. With something very simple like Node-RED, you can adjust the limits as you want according to the information received on the topic MQTT_PUBLISH_TOPIC_BAT. You can also turn off the power when the mac goes to sleep and turn it back on when it has woken up (MQTT_PUBLISH_TOPIC_INFO).

Need cmake and pkg-config:

$ brew install pkg-config
$ brew install cmake

depends on:

• CoreFoundation and IOKit (XCode)
• mosquitto

$ brew install mosquitto

• Modify batt2mqtt.plist to fit your needs (replace the XXXX). You can safely remove the section EnvironmentVariables if you don't use a user/password to connect to your broker (MQTT server)
• Modify what you want in src/batt2mqtt.c between BEGIN and END tags to set informations about your broker and topics.

Messages received on this topic are:

• willsleep when the laptop will go to sleep
• haspoweredon when the laptop woke up

Message format: string

Message received on this topic is for example:

• {"percentage":51, "state":0}

where percentage is the battery level and state is the power source status (0 = discharging (on Battery), 1 = charging (on Power AC))

Message format: JSON

You can send 2 commands to your mac (cf topic MQTT_SUBSCRIBE_TOPIC_CMD in src/batt2mqtt.c) :

• displaysleepnow (causes display to go to sleep immediately)
• sleepnow (causes an immediate system sleep)

Message format: string

$ mkdir build
$ cd build
$ cmake ..
$ make
$ make install

This will install batt2mqtt as an agent.

If you want to see the logs, use log.
Eg (like tail -f):

$ log stream --predicate 'subsystem contains "conurb.batt2mqtt"' --info --debug --style compact

or, for example, show the logs from the past 2 hours:

$ log show --predicate 'subsystem contains "conurb.batt2mqtt"' --info --debug --style compact --last 2h