macOS Quirks: Bluetooth Device Battery Low

For some reason, macOS has a very low threshold set for bluetooth batteries (such as the Magic Mouse & Keyboard). Believe it or not, it's set to 2%. To me, that's a bit too close to death to let me know its battery is getting low and I needed more warning than that - especially given that the Apple Magic Mouse 2's Lightning port is on the bottom of the mouse. Charging it is not something I can do while I'm trying to work.

I searched around and could not find a setting or even a plist entry to change that. Luckily a lot of things within macOS is accessible through command line tools. The main tool we can use to access this information is ioreg (the I/O Registry).

I wrote a couple of bash scripts to work-around this issue, one for the mouse and another for the keyboard.

#!/bin/sh
PATH=/usr/local/bin:/usr/local/sbin:~/bin:/usr/bin:/bin:/usr/sbin:/sbin

# Script that checks the battery level of a connected mouse and displays a notification if it is below a threshold (default 15%). Can set threshold as a parameter. ex: ./check_mouse_battery.sh 10

MOUSENAME=`ioreg -c AppleDeviceManagementHIDEventService -r -l | grep -i mouse | cut -d = -f2 | cut -d \" -f2`

MOUSEBATTERY=`ioreg -c AppleDeviceManagementHIDEventService -r -l | grep -i mouse -A 20  | grep BatteryPercent | cut -d = -f2 | cut -d ' ' -f2`

COMPARE=${1:-15}

if [ -z "$MOUSEBATTERY" ]; then
    echo 'No Mouse Found.'
    exit 0
fi

if (( MOUSEBATTERY < COMPARE )); then
    osascript -e "display notification \"Battery Level at ${MOUSEBATTERY}%.\" with title \"Battery Low\" subtitle \"${MOUSENAME}\""
fi

The script(s) essentially:

1. Grabs the name of the device MOUSENAME & its battery percentage MOUSEBATTERY.
2. Sets the value of COMPARE to the first script argument or the default (15).
3. If no device is found, it exits the script.
4. If MOUSEBATTERY is less than COMPARE, displays a Notification in macOS with the current battery level.

Then I had to set up a way to automate running the script at regular intervals. For this I am using launchctl and instructions for setting that up is included in the repository for this utility below. I have the plist for it configured to run the script every 2 hours.

To keep the script simple, I separated checking the mouse & keyboard into different files. Getting around that annoyance was a fun exercise in itself and I may actually look forward to the next time I get the warning to charge my devices soon.

Github Repository