BCLM is a wrapper to read and write battery charge level max (BCLM) values to the System Management Controller (SMC) on Mac computers. This project was inspired by several battery management solutions, including Apple's own battery health management.

The purpose of limiting the battery's max charge is to prolong battery health and to prevent damage to the battery. Various sources show that the optimal charge range for operation of lithium-ion batteries is between 40% and 80%, commonly referred to as the 40-80 rule [1][2][3]. This project is especially helpful to people who leave their Macs on the charger all day, every day.

BCLM is written in Swift and is trivial to compile. A release zip is also provided with a signed and notarized binary for those who do not have development tools and Xcode.

$ swift build
$ sudo swift test
$ cp .build/debug/bclm /usr/local/bin

$ unzip bclm.zip
$ cp bclm /usr/local/bin

$ bclm
OVERVIEW: Battery Charge Level Max (BCLM) Utility.

USAGE: bclm <subcommand>

OPTIONS:
  --version               Show the version.
  -h, --help              Show help information.

SUBCOMMANDS:
  read                    Reads the BCLM value.
  write                   Writes a BCLM value.

  See 'bclm help <subcommand>' for detailed help.

When writing values, macOS charges slightly beyond the set value (~3%). In order to display 80% when fully charged, it is recommended to set the BCLM value to 77%.

$ sudo bclm write 77
$ bclm read
77

Note that in order to write values, the program must be run as root. This is not required for reading values.

The SMC can be reset by a startup shortcut or various other technical reasons. To ensure that the BCLM is always at its intended value, it should be run at startup via launchd as root.

$ sudo cp com.zackelia.bclm.plist /Library/LaunchDaemons
$ sudo launchctl load /Library/LaunchDaemons/com.zackelia.bclm.plist

Note that the provided plist sets the BCLM to 80%. This can be changed in the ProgramArguments key.