Forcing the 80% battery limit on ARM macs using fish 🐟

README.md

See the instructions on install smc here, then append the snippet below to your ~/.config/fish/config.fish, if you use fish instead of the z shell.

Credit for rewriting to the fish syntax goes to ChatGPT 🙃

battery_limit.fish

# Apple Silicon laptops with firmware > 13.0 have a native charge threshold that does not require any userspace daemon.
# This native limit works even when the laptop is sleeping or powered off, making it preferable to the userspace daemon.
# However, it only supports fixed thresholds (80% as upper limit and 70% as lower limit).
# The CHWA key is used to enable/disable the native limit. 01 = 80% limit, 00 = no limit
##
set -g smc_command "/usr/local/bin/smc"
set -g smc_charge_limit_key "CHWA"
set -g smc_charge_limit_status_on "01"
set -g smc_charge_limit_status_off "00"

function battery-charge-limit-enable
	if test (uname) = "Darwin"
		if not test -e $smc_command
			echo 'SMC command not found!'
			return 1
		end

		sudo $smc_command -k $smc_charge_limit_key -w $smc_charge_limit_status_on
	else
		echo "Not a Darwin system."
	end
end

function battery-charge-limit-disable
	if test (uname) = "Darwin"
		if not test -e $smc_command
			echo 'SMC command not found!'
			return 1
		end

		sudo $smc_command -k $smc_charge_limit_key -w $smc_charge_limit_status_off
	else
		echo "Not a Darwin system."
	end
end

function battery-charge-limit-status
    if test (uname) = "Darwin"
        if not test -e $smc_command
            echo 'SMC command not found!'
            return 1
        end

        # Run the smc command and capture its output
        set status_raw (sudo $smc_command -k $smc_charge_limit_key -r)

        # Extract the status value from the output
        if string match -rq 'CHWA\s+\[flag\]\s+\(bytes\s+([0-9a-fA-F]+)\)' -- $status_raw
            set -l status_value (string match -r 'CHWA\s+\[flag\]\s+\(bytes\s+([0-9a-fA-F]+)\)' -- $status_raw)
            set status_value $status_value[2]  # Extract the matched group

            switch $status_value
                case $smc_charge_limit_status_on
                    echo "Charge limit is enabled (80%)."
                case $smc_charge_limit_status_off
                    echo "Charge limit is disabled (no limit)."
                case '*'
                    echo "Unknown $smc_charge_limit_key status: $status_value"
            end
        else
            echo "Unable to determine charge limit status."
        end
    else
        echo "Not a Darwin system."
    end
end