Systemd Battery Monitor Service

battmon.service

# This file goes into /etc/systemd/system/battmon.service
[Unit]
Description=suspend when batt < 10%

[Service]
Type=oneshot
ExecStart=/usr/local/bin/battmon.sh
User=root

battmon.sh

#!/bin/sh
# This file goes into /usr/local/bin/battmon.sh
acpi -b | awk -F'[,:%]' '{print $2, $3}' | {
	read -r status capacity

	if [ "$status" = Discharging -a "$capacity" -lt 10 ]; then
		logger "Critical battery threshold"
		systemctl suspend
	fi
}

battmon.timer

# This file goes into /etc/systemd/system/battmon.timer
[Unit]
Description=Run battmon every minute

[Timer]
OnCalendar=minutely
Persistent=true     
 
[Install]
WantedBy=timers.target