battery-monitor.sh - A simple battery monitor script which sends desktop notifications when your battery level reaches predefined thresholds

battery-monitor.service

# $HOME/.config/systemd/user/battery-monitor.service
# Then: systemctl daemon-reload && systemctl enable --now --user battery-monitor.service
[Unit]
PartOf=graphical-session.target
After=graphical-session.target
Requisite=graphical-session.target

[Service]
ExecStart=%h/.local/bin/battery-monitor
Restart=on-failure

[Install]
WantedBy=graphical-session.target

battery-monitor.sh

#!/bin/bash
# battery-monitor.sh - A simple battery monitor script which sends desktop
# notifications when your battery level reaches pre-defined thresholds
# Install to $HOME/.local/bin

declare -A LAST_NOTIFIED
CHECK_INTERVAL=33
THRESHOLDS=(5 10 15 20)

notify() {
    notify-send "Battery Low" "Battery level is $2%"
}

while true; do
    BATTERIES=(/sys/class/power_supply/BAT*)

    for BATTERY_PATH in "${BATTERIES[@]}"; do
        BATTERY=$(basename "$BATTERY_PATH")

        charge_now=$(cat "$BATTERY_PATH/charge_now")
        charge_full=$(cat "$BATTERY_PATH/charge_full")
        percentage=$((charge_now * 100 / charge_full))
        status=$(cat "$BATTERY_PATH/status")

        if [ "$status" = "Discharging" ]; then
            for threshold in "${THRESHOLDS[@]}"; do
                # Only notify once for a specific threshold until the battery begins charging
                if [ $percentage -le $threshold ]; then
                    if  [ "${LAST_NOTIFIED[$BATTERY]}" != "$threshold" ]; then
                        LAST_NOTIFIED[$BATTERY]=$threshold  # Track that this battery hit this threshold
                        notify "$BATTERY" "$percentage"
                    fi
                    break
                fi
            done
        elif [ "$status" = "Charging" ] || [ "$status" = "Full" ]; then
            # Reset LAST_NOTIFIED when battery starts charging or is full
            unset LAST_NOTIFIED[$BATTERY]
        fi
    done

    sleep $CHECK_INTERVAL
done