Here's exactly how your iPhone gets slower when you have an old battery — and how to replace it (AAPL)

Apple on Thursday apologized because some customers were upset that it slowed down iPhones with older batteries.
Older iPhones can take longer to launch apps, may display choppy scrolling, and can have dimmer screens and quieter speakers.
According to Apple, it's a "power management" feature that helps protect the iPhone from random shutdowns and damage to its components.
Apple began offering its $29 in-store battery replacements on Saturday.

If your iPhone is getting on in age, you may have noticed it runs slower after the latest updates.

That's because Apple slows down iPhones with aging batteries, the company recently disclosed. According to Apple, software updates throttle older iPhones because their batteries are "less capable of delivering peak energy loads," according to an apology the company issued Thursday.

If you're wondering what slower performance means for your iPhone, Apple posted a help document outlining exactly what its "power management" does. Meanwhile, the company launched a $29 in-store battery replacement service on Saturday, allowing those looking to speed up their iPhone a cheaper way to swap out an aging battery.

If your phone has a really old battery, Apple says, your phone may take longer to launch apps and may display apps at lower frame rates — meaning you get a choppy user experience.

Here's the full list of reductions in performance your iPhone may see with an old battery:

Apple also provided a list of features it said would not be affected on older iPhones:

How to fix it

Here's Apple's technical explanation for its power-management software:

"This power management works by looking at a combination of the device temperature, battery state of charge, and the battery's impedance. Only if these variables require it, iOS will dynamically manage the maximum performance of some system components, such as the CPU and GPU in order to prevent unexpected shutdowns.

"As a result, the device workloads will self-balance, allowing a smoother distribution of system tasks, rather than larger, quick spikes of performance all at once. In some cases, a user may not notice any differences in daily device performance. The level of perceived change depends on how much power management is required for a particular device."

This basically means that an iPhone with an older battery can't provide enough power to operate at full capacity without hurting the iPhone's components. When an iPhone realizes the battery may not provide enough voltage and could hurt its parts, it automatically shuts down. That's a feature, according to Apple.

So Apple programmed a new piece of software that would prevent the iPhone from taking full advantage of its components. Instead of letting the iPhone run at full power, Apple instead has its phones "self-balance" and take a little longer to complete tasks.

The good news is that replacing the battery on your iPhone 6, iPhone 6S, or iPhone 7 should help it get back to full strength. If you're unsure whether your battery is old, Apple will release a software update that will let you check on its health. For the next year, Apple is charging only $29 for a battery replacement at one of its stores. That reduced pricing went into effect on Saturday, a bit sooner than planned, Apple's Trudy Muller told Business Insider.

"We expected to need more time to be ready, but we are happy to offer our customers the lower pricing right away. Initial supplies of some replacement batteries may be limited."

Here's exactly how your iPhone gets slower when you have an old battery — and how to replace it (AAPL)

How to fix it

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