How Apple works around the limits of battery harmony with fast charging and optimal battery charging

The most important limitation of mobile devices is power. Engineers continue to find ways to cram more transistors into chips, but batteries have hit a wall of physics, forcing device makers like Apple to come up with innovative solutions to these limitations.

The underlying problem is that lithium-ion – the current chemistry of the battery of choice – is not particularly stable. It’s more forgiving than older technologies like nickel-cadmium, but it’s very easy to shorten the life of a lithium-ion battery by:

  • Completely drain the battery
  • Battery retention at 100% charge level
  • Letting the battery heat up

Users have two opposing desires regarding batteries, whether they realize it or not. In the short term, they want the device to always be charged and ready to use—there’s nothing more frustrating than running out of power sooner than you might expect in a day. In the long run, they want the battery to maintain its capacity for as long as possible – replacing the battery to return the device to a decent daily battery life is expensive and annoying.

In an effort to satisfy each of these conflicting desires, Apple has developed two seemingly contradictory technologies: fast charging, which does what it says, and Enhanced Battery Charging, which actually makes the battery charge slower.

fast charging

Some Apple devices — most notably the iPhone 8 and later, USB-C iPad models, and 14-inch and 16-inch MacBook Pro models — support fast charging, which can charge the battery up to 50% in 30 minutes.

Fast charging requires a powerful charger and appropriate cable – it does not work with MagSafe and Qi wireless chargers. For each group of devices you need:

  • Iphone: At least 18W (20W for iPhone 12) USB-C power adapter that supports USB Power Delivery (USB-PD), plus USB-C to Lightning cable (no other cable can be used)
  • iPads: USB-C charger at least 30W with USB-C cable
  • The 14-inch MacBook Pro: At least 96W power adapter plus Thunderbolt cable, USB-C or MagSafe 3, or external monitor with 94W power delivery via Thunderbolt 3 or USB-C
  • MacBook Pro 16-inch: 140W Power Adapter Plus USB-C to MagSafe 3 . Cable

Fast charging works by delivering more power to the device from the adapter. But with great power comes great the responsibilityHeat, leading some to believe that fast charging shortens battery life. Marks Brownlee explains that fast charging does not usually reduce battery life much, if anything, due to a variety of technologies that reduce the amount of heat generated.

But fast charging only takes up to 50% battery. To get the rest of the way in a way that doesn’t result in your battery staying at 100% for too long, Apple has developed the Optimized Battery Charging feature.

Optimized battery charging

Batteries don’t like to be kept at 100%, but users want their batteries to be at 100% when they start the day. How is Apple going in this line? Starting with iOS 13, iPadOS 13, and macOS 10.15.5 Catalina, Apple introduced features to reduce the maximum charge to extend battery life. The first is the improved battery charging.

Optimized Battery Charging uses machine learning to guess when and where you charge your devices the most, keeping your battery at 80% until you think you need to be at 100%.

In a TidBITS Talk, David C. gave a great technical explanation of Enhanced Battery Charging:

Apple’s Optimized Battery Charging is a difference in this regard. It uses constant current charging until the battery charge reaches about 80%. Then instead of doing a constant voltage constant voltage it will dynamically set the voltage so it hits 100% shortly before you think you’re going to remove the device from the charger. For example, if your usage history says you removed it from the charger at 8:00 AM every morning, it might try to reach 100% at 5:30 AM, even though a conventional DC charger might be able to Bring it to 100% at 2:00 AM.

In theory, you should never notice this feature because it works while you sleep. In About the improved battery charging on your iPhone, Apple says:

Your iPhone uses machine learning on the device to learn your daily charging routine so that Optimized Battery Charging only activates when your iPhone expects to be connected to a charger for an extended period of time. The algorithm aims to ensure that your iPhone is still fully charged when it is unplugged.

Enhanced Charging is designed to only share in the locations where you spend the most time, like your home and workplace. This feature does not react when your usage habits are more changing, as when traveling.

Enhanced battery charging is location specific, as you can tell by the fact that Apple specifies that the following settings must be enabled for them to work on your iPhone:

  • Settings>Privacy>Location Services>Location Services
  • Settings>Privacy>Location Services>System Services>System Customization
  • Settings > Privacy > Location Services > System Services > Significant Sites > Significant Sites

When you enable Optimized Battery Charging on your iPhone, a notification appears on your screen. To bypass it and charge the battery fully, 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 start the day regularly with less than a full charge.

Enhanced Battery Charging works a little differently on Mac laptops. If you click on the battery icon in the menu bar, you may see Charging is on hold. You can tap Charge to Full Now to bypass the optimized battery charge.

Ship to full macOS

To turn the feature off, go to System Preferences > Battery > Battery and uncheck Optimized Battery Charging. You can disable it permanently or just for one day. Again, only do this if you are a regular on the go with the feature.

Optimized battery charging on macOS

Battery health management

In addition to improved battery charging, iPhones and iPads have a charge management feature that temporarily reduces the maximum battery charge capacity when devices are constantly connected to power. Apple says:

iPad with iOS 11.3 or later and iPhone XS, iPhone XS Max, or iPhone XR with iOS 12 or later have a charge management feature to help maintain battery health, which monitors these devices for use in these charging states and, where appropriate, reduces the maximum capacity for the battery. The battery indicator will display the charge percentage based on this adjusted maximum capacity. Maximum capacity will revert back to the unadjusted level when your iPad or iPhone is not connected to power for extended periods and as conditions and battery health permit.

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 a little differently on M1-based Macs and Intel-based Macs.

On M1-based Macs, macOS will temporarily reduce the maximum battery capacity to extend battery life:

Battery Health Management is designed to improve battery life by chemically reducing the rate of battery aging. The feature does this by monitoring a history of the battery’s temperature and charging patterns.

Based on the measurements you collect, Battery Health Management may temporarily reduce the maximum battery charge. This happens as needed to ensure the battery is charged to the optimum level for your use – reducing battery wear and slowing its chemical aging.

You can’t 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 life. Again, we generally recommend not disabling it, but if it’s preventing you from charging to the level you need at a certain point in time, it may be worth turning it off.

Set up battery longevity management in macOS

In the end, as frustrating as it is that battery technology hasn’t developed in parallel with the computational capabilities of our devices, it’s good to see that Apple is using some of its processing power to get the most out of what our batteries can do.

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