If you are reading this story, you likely have an iPhone or a Mac that you would like to use for as long as possible.

Unfortunately, both iPhone and Mac devices have batteries that are not user-serviceable even though they are consumables and have limited lifespan.

According to research, lithium batteries should ideally be charged to a maximum of 80% of their capacity and discharged to a minimum of 20% to increase their lifespan.

Electric car batteries should not, generally, be charged to 100%. Long-term, this reduces the battery's longevity, and Tesla cars actually charge up to 90% by default. Mashable

So really, if you were super-keen on keeping your battery living as long as possible, you should keep its charge between 20 and 80 per cent. Wired

As a result, Apple has implemented a feature called Optimized Battery Charging available and enabled by default starting on iOS 13 and macOS Big Sur (requires “Location Services” which isn’t great for privacy).

When Apple Silicon MacBook Air or Pro is chronically plugged in (when using a dock for example), Optimized Battery Charging is supposed to pause charging when battery is charged to 80% to preserve its lifespan.

Problem is… it doesn’t. At least this is what I noticed on my M1 MacBook Air (corroborated on my girlfriend’s M1 MacBook Air) when I investigated why capacity of battery was at 89% after only 50 charging cycles.

Heads-up: to contribute to project, please share cycle count, maximum capacity and purchase date of your Mac in the comments of YouTube episode.

To find cycle count and maximum capacity, run following command (without the $) in “Terminal” app.

$ system_profiler SPPowerDataType | grep -E "Cycle Count|Maximum Capacity" | awk '{printf "%s ",$3}'
50 89%

To find purchase date, please go to https://checkcoverage.apple.com/, enter serial number and hit “Submit”.

Another common (and very expensive) issue with chronically plugged in Macs is swollen batteries. To be fair, this is not an Apple-specific issue but rather one related to Lithium batteries in general. That said, I believe Apple could easily do something about it such as asking users to discharge battery to 20% once in a while.

When I say easily, I mean it… here is how one can discharge battery of Apple Silicon Macs to 20% while plugged in (using a secret trick).

Caveats

• When copy/pasting commands that start with $, strip out $ as this character is not part of the command
• When copy/pasting commands that start with cat << "EOF", select all lines at once (from cat << "EOF" to EOF inclusively) as they are part of the same (single) command

Setup guide

Shout-out to actuallymentor for opening my eyes (use at your own risk, may void warranty)

Step 1: install Xcode Command Line Tools

$ xcode-select --install

Step 2: clone smcFanControl GitHub repository

$ git clone https://github.com/hholtmann/smcFanControl

Step 3: create /usr/local/bin directory

$ sudo mkdir -p /usr/local/bin

Step 4: compile and install smc command

$ cd smcFanControl/smc-command

$ make

$ sudo cp smc /usr/local/bin/

Step 5: create discharge.sh convenience script

$ cat << "EOF" | sudo tee /usr/local/bin/discharge.sh
#! /bin/sh

function cancel()
{
  printf "\n"
  sudo smc -k CH0I -w 00
  exit 0
}

trap cancel INT

bold=$(tput bold)
red=$(tput setaf 1)
normal=$(tput sgr0)

target=20

sudo smc -k CH0I -w 01

printf "$bold$red%s$normal\n" "Discharging battery to $target% (press ctrl+c to cancel)"

while [ $(pmset -g batt | grep --extended-regexp --only-matching "\d+%" | cut -d% -f1) -gt $target ]; do
  sleep 60
done

cancel
EOF

Step 6: make discharge.sh executable

$ sudo chmod +x /usr/local/bin/discharge.sh

Usage guide

$ discharge.sh
Discharging battery to 20% (press ctrl+c to cancel)