Reprinted from TidBITS by permission; reuse governed by Creative Commons
license BY-NC-ND 3.0. TidBITS has offered years of thoughtful commentary
on Apple and Internet topics. For free email subscriptions and access to the
entire TidBITS archive, visit http://www.tidbits.com/
How Apple Works Around Battery Chemistry Limits with Fast Charge and Optimized
Battery Charging
Josh Centers
The most significant limitation for mobile devices is power. Engineers
keep finding ways to cram more transistors into chips, but batteries
have hit a brick wall of physics, forcing hardware makers like Apple to
invent creative workarounds for those limitations.
The inherent problem is that lithium-ion'the current battery chemistry
of choice'isn't particularly stable. It's more forgiving than older
technologies like nickel-cadmium, but [1]it's all too easy to shorten a
lithium-ion battery's lifespan by:
* Draining the battery completely
* Holding the battery at a 100% charge level
* Letting the battery get hot
Users have two conflicting desires with regard to batteries, whether or
not they realize it. In the short term, they want the device always
charged and ready to use'little is more frustrating than running out of
power earlier than you'd expect in a day. Long-term, they want the
battery to maintain its capacity for as long as possible'replacing a
battery to bring a device back to decent daily battery life is
expensive and annoying.
In an effort to meet both of these conflicting desires, Apple has
developed two seemingly contradictory technologies: fast charge, which
does what it says, and Optimized Battery Charging, which actually makes
the battery charge more slowly.
Fast Charge
Certain Apple devices'most [2]notably the iPhone 8 and later, [3]USB-C
iPad models, and [4]14-inch and 16-inch MacBook Pro models'support fast
charge, which can charge the battery up to 50% in 30 minutes.
Fast charge requires a sufficiently powerful charger and appropriate
cable'it does not work with wireless MagSafe and Qi chargers. For each
of the device families, you need:
* iPhones: At least an 18-watt (20-watt for the iPhone 12) USB-C
power adapter that supports USB Power Delivery (USB-PD), plus a
USB-C to Lightning cable (not that any other cable is possible)
* iPads: At least a 30-watt USB-C charger with a USB-C cable
* 14-inch MacBook Pro: At least a 96-watt power adapter plus a
Thunderbolt, USB-C, or MagSafe 3 cable, or an external display with
94-watt power delivery via Thunderbolt 3 or USB-C
* 16-inch MacBook Pro: A 140-watt power adapter plus a USB-C to
MagSafe 3 cable
Fast charge works by delivering more power to the device from the
adapter. But with great power comes great [DEL: responsibilty :DEL]
heat, leading some to believe that fast charge actually shortens your
battery life. Marques Brownlee explains that [5]fast charge doesn't
typically reduce your battery life by much, if at all, due to a variety
of techniques that reduce the amount of heat generated.
IFRAME: [6]https://www.youtube.com/embed/UpqaQR4ikig?feature=oembed
But fast charge only takes a battery to 50%. To get the rest of the way
in a manner that doesn't result in the battery sitting at 100% for a
long time, Apple developed Optimized Battery Charging.
Optimized Battery Charging
Batteries don't like being held at 100%, but users want their batteries
to be at 100% when they start the day. How does Apple walk that line?
Starting with iOS 13, iPadOS 13, and macOS 10.15.5 Catalina, Apple has
provided features to reduce the maximum charge to extend the battery's
life. The first is Optimized Battery Charging.
Optimized Battery Charging uses machine learning to guess when and
where you charge your devices the most and hold the battery's charge at
80% until it thinks you need it to be at 100%.
On TidBITS Talk, David C. provided [7]a great technical explanation of
Optimized Battery Charging:
Apple's optimized battery charging is a variation on this. It uses
constant current charging until the battery's charge reaches about
80%. Then instead of doing constant-voltage at a fixed voltage, it
will dynamically select voltages so it will reach 100% shortly
before it thinks you will remove the device from the charger. For
example, if your usage history says you remove it from the charger
at 8:00am every morning, it might try to reach 100% at 5:30am, even
though a traditional constant-voltage charger might be able to bring
it to 100% at 2:00am.
In theory, you should almost never notice this feature because it works
while you're asleep. In [8]About Optimized Battery Charging on your
iPhone, Apple says:
Your iPhone uses on-device machine learning to learn your daily
charging routine so that Optimized Battery Charging activates only
when your iPhone predicts it will be connected to a charger for an
extended period of time. The algorithm aims to ensure that your
iPhone is still fully charged when unplugged.
Optimized charging is designed to engage only in locations where you
spend the most time, such as your home and place of work. The
feature doesn't engage when your usage habits are more variable,
such as when you travel.
Optimized Battery Charging is location-specific, as you can tell by the
fact that Apple specifies that the following settings must be enabled
for it to work on an iPhone:
* Settings > Privacy > Location Services > Location Services
* Settings > Privacy > Location Services > System Services > System
Customization
* Settings > Privacy > Location Services > System Services >
Significant Locations > Significant Locations
When Optimized Battery Charging is enabled on an iPhone, a notification
appears on your screen. To bypass it and fully charge your battery,
touch and hold the notification and tap Charge Now. You can also turn
off Optimized Battery Charging in Settings > Battery > Battery Health,
but that's probably a bad idea unless you're regularly starting the day
with less than a full charge.
[9]Optimized Battery Charging works slightly differently on Mac
laptops. If you click the battery icon in the menu bar, you may see
Charging on Hold. You can click Charge to Full Now to override
Optimized Battery Charging.
To turn off the feature, go to System Preferences > Battery > Battery
and uncheck Optimized Battery Charging. You can disable it permanently
or just for a day. Again, don't do this unless you're regularly butting
heads with the feature.
Battery Health Management
Beyond Optimized Battery Charging, iPhones and iPads have a [10]charge
management feature that temporarily reduces the battery's maximum
charge capacity when devices are constantly plugged into power. Apple
says:
iPad with iOS 11.3 or later and iPhone XS, iPhone XS Max, or iPhone
XR with iOS 12 or later include a charge management feature to help
maintain battery health, which monitors these devices for use in
these charging situations and, as required, reduces the maximum
capacity of the battery. The battery indicator will display the
charge percentage based on this adjusted maximum capacity. The
maximum capacity will revert back to the nonadjusted level when iPad
or iPhone is no longer connected to power for prolonged periods and
as conditions and battery health allow.
On iPhones and iPads, this charge management feature is automatic, and
you can't turn it off.
Apple calls a similar feature on Macs 'battery health management.' It
works slightly differently on [11]M1-based Macs and [12]Intel-based
Macs.
On M1-based Macs, macOS will temporarily reduce your battery's maximum
charge capacity to extend the battery's lifespan:
Battery health management is designed to improve your battery's
lifespan by reducing the rate at which it chemically ages. The
feature does this by monitoring your battery's temperature history
and its charging patterns.
Based on the measurements that it collects, battery health
management may temporarily reduce your battery's maximum charge.
This happens as needed to ensure that your battery charges to a
level that's optimized for your usage'reducing wear on the battery,
and slowing its chemical aging.
You cannot disable the feature on M1-based Macs, but you can on
Intel-based Macs by going to System Preferences > Battery > Battery >
Battery Health and unchecking Manage Battery Longevity. Again, we
generally recommend against disabling it, but if it's preventing you
from charging to the level you need at a particular time, it might be
worthwhile to turn it off.
In the end, as frustrating as it is that battery technology hasn't
evolved in step with the computational capabilities of our devices,
it's nice to see that Apple is using some of that processing power to
make the most of what our batteries can do.
References
Visible links
1. https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries
2. https://support.apple.com/en-us/HT208137
3. https://support.apple.com/en-us/HT209186
4. https://support.apple.com/en-us/HT212755
5. https://www.youtube.com/watch?v=UpqaQR4ikig
6. https://www.youtube.com/embed/UpqaQR4ikig?feature=oembed
7. https://talk.tidbits.com/t/optimised-battery-charging-help/18795/2?u=jcenters
8. https://support.apple.com/en-us/HT210512
9. https://support.apple.com/en-us/HT212049
10. https://support.apple.com/en-us/HT208710
11. https://support.apple.com/en-us/HT211832
12. https://support.apple.com/en-us/HT211094
Hidden links:
13. https://i0.wp.com/tidbits.com/wp/../uploads/2022/05/Optimized-battery-charging.jpeg?ssl=1
14. https://i0.wp.com/tidbits.com/wp/../uploads/2022/05/macOS-charge-to-full.png?ssl=1
15. https://i0.wp.com/tidbits.com/wp/../uploads/2022/05/Optimized-battery-charging-macOS.png?ssl=1
16. https://i0.wp.com/tidbits.com/wp/../uploads/2022/05/Battery-longevity.png?ssl=1