January 2022 • Macworld 75most people, macOS will manage
charging better than we can and
with zero effort.
Before Big Sur, macOS charged
a laptop to 100 per cent power
whenever it was plugged in and kept
charging it to make sure it stayed at
that level. That can be useful during
the times you need your laptop
topped off, something that was true
when various MacBooks couldn’t
make it through a day of use, and for
many people before the pandemic.
But recharge time is relatively fast
compared to discharge, and most
of us don’t use our laptops while
asleep Why charge to 100 per cent
and stress the battery, keeping it
there during the several hours we’re
asleep? Or if we don’t need 100 per
cent to get through the times we’re
not plugged in? This is especially
the case with M1-based laptops,
which are absurdly power efficient.
The maximum capacity of a
lithium-ion (Li-ion) battery is an
estimate of how much it can be safely
charged. The charging system in any
sensible device that uses a Li-ion
battery monitors feedback as it feeds
it electricity, including temperature
sensors. The system reduces what
it considers ‘100 per cent’ on that
battery over time to avoid damage
and even fire.
The trick is to charge a battery
just enough all the time to meet your
needs without keeping it at a level that
produces enough heat to degrade the
battery’s life. This is the Big Sur and
Monterey strategy.
Big Sur adopted changes already
brought to iOS and iPadOS that
charge your battery to 80 per cent for
periods when the operating system
has determined you don’t need a full
charge. It then kicks in to charge to
100 per cent with some margin of time
before it estimates you’ll take the
device off power and use it on battery
for an extended period.
Starting in Big Sur, the overhauled
Battery preference pane’s Battery
view offers a lot of tweaks about
how macOS consumes and charges
a battery. The key one? ‘Optimized
battery charging’. When checked,
macOS watches your usage
behaviour so it doesn’t charge past
80 per cent if it doesn’t anticipate that
you need to remove power from your
laptop in the near future. The 80 per
cent threshold is where chargers stop
performing a quick charge on most
Li-ion batteries and slow to avoid
overheating them.
I’ve found in my normal usage
with an M1 MacBook Air at home, it