macbook-charge-limit

Set an Intel MacBook battery charge limit from Linux.

The tool writes the Apple SMC BCLM and BFCL keys. It is intended for Intel MacBooks where those keys exist, but Linux does not expose a standard charge_control_end_threshold battery setting.

Supported Hardware

Tested on:

• Apple MacBookAir6,2
• Linux 7.0.0-1-cachyos

The program refuses to run unless DMI reports Apple Inc. and a product name starting with MacBook. It does not expose arbitrary SMC writes.

Get The Source

Clone the repository:

git clone https://github.com/jtbrough/macbook-charge-limit.git
cd macbook-charge-limit

Build:

make

Use Without Installing

Read the current SMC values:

sudo ./macbook-charge-limit read

Set a limit:

sudo ./macbook-charge-limit set 80

Reset to full charge:

sudo ./macbook-charge-limit reset

Valid limits are 20..100.

Install

sudo make install
sudo systemctl daemon-reload
sudo systemctl enable --now macbook-charge-limit.service

Installed files:

/usr/local/bin/macbook-charge-limit
/etc/macbook-charge-limit.conf
/etc/systemd/system/macbook-charge-limit.service

make install does not overwrite an existing config file.

Configure

Edit:

/etc/macbook-charge-limit.conf

Example:

LIMIT=80

Apply a config change:

sudo systemctl restart macbook-charge-limit.service

Check the configured value:

sudo macbook-charge-limit read

Expected output for an 80% limit:

BCLM=80 BFCL=80

Verify Charging Behavior

The limit does not discharge a full battery down to the target. To verify it, drain below the configured limit, plug in AC, and watch the battery stop near the limit:

watch -n 10 'printf "AC="; cat /sys/class/power_supply/ADP1/online; for f in status capacity charge_now charge_full current_now voltage_now; do printf "%s=" "$f"; cat "/sys/class/power_supply/BAT0/$f"; done'

When the limit is honored, AC is connected, current_now is 0, and status is usually Full or Not charging.

Update

git pull
make
sudo make install
sudo systemctl daemon-reload
sudo systemctl restart macbook-charge-limit.service

Uninstall

Reset the SMC limit before removing the binary if you want normal 100% charging:

sudo macbook-charge-limit reset

Disable the service and remove installed files:

sudo systemctl disable --now macbook-charge-limit.service
sudo make uninstall
sudo systemctl daemon-reload

Remove the config if it is no longer needed:

sudo rm -f /etc/macbook-charge-limit.conf

Notes

This is a userspace workaround. Native desktop integration depends on a kernel driver exposing the standard power-supply threshold interface.

Upstream Progress

This tool exists because Linux has no native way to set a MacBook's charge limit. That's being worked on upstream, and this section tracks it. Once the kernel and UPower changes below land in a released distro, this project becomes unnecessary for most users.

Pending review:

• [PATCH v2 0/2] hwmon: (applesmc) add charge_control_end_threshold support
• upower!346: prefer live sysfs threshold values over hwdb CHARGE_LIMIT default

The two kernel patches add real charge_control_end_threshold sysfs support to applesmc, backed by the actual Apple SMC BCLM key. The UPower change fixes a separate bug where UPower (and anything reading its D-Bus property, like KDE's battery applet) shows a static default instead of the real configured threshold.