# /etc/systemd/system/battery-charge-limit.service
[Unit]
Description=Set the battery charge threshold
After=multi-user.target
StartLimitBurst=10

[Service]
Type=oneshot
ExecStartPre=/usr/bin/test -f /sys/class/power_supply/BAT0/charge_control_end_threshold
ExecStart=/bin/bash -c 'echo 80 > /sys/class/power_supply/BAT0/charge_control_end_threshold'
RestartSec=15s
Restart=on-failure

[Install]
WantedBy=multi-user.target