Simple battery checker notify script and systemd service/timer for barebones WM setups. By default this script alerts at < 30 minutes of estimated battery remaining, see below to customize this.
The following packgaes must be installed: acpi, notify-osd. For notifications, dunst is recommended and should be started alongside your window manager. Consult your distribution on how to install these packages.
If you do not have root access and cannot copy check-battery.sh to /usr/local/bin/, install it to a local path and update the ExecStart= parameter in the systemd unit file before copying it.
git clone https://github.com/clukawski/check-battery
cd check-battery
mkdir -p ~/.config/systemd/user/
sudo cp check-battery.sh /usr/local/bin/
cp check-battery.timer check-battery.service ~/.config/systemd/user/
systemctl --user daemon-reload
systemctl --user enable --now check-battery.timer
Adjust the following line in check-battery.sh to customize when the alert for time remaining fires (in hours, minutes, and seconds). Default is 30 minutes.
TIME_REMAINING="00:30:00"