Only part of that is true: Older iPhones with aged batteries *are* more sluggish than new phones — but Apple claims it's because they're trying to avoid forced, unexpected shut downs, not because they want you to upgrade.
Robert Galbraith / Reuters
Basically, iPhones use lithium-ion batteries, which decay over time.
After 500 charge cycles, the iPhone battery is designed to retain only 80% of its original capacity. So depending on use, you may start to see your iPhone's battery life dwindle after a year or so.
As the battery degrades, it can no longer handle demanding tasks, like processor-intensive games and apps.
So, for iPhone 6, 6S, SE, and 7, Apple recently released a feature that throttles — or slows down — the iPhone's processor when it's running on a decayed battery. This is to prevent your iPhone from malfunctioning and shutting down.
In a statement to BuzzFeed News, Apple said:
"Our goal is to deliver the best experience for customers, which includes overall performance and prolonging the life of their devices. Lithium-ion batteries become less capable of supplying peak current demands when in cold conditions, have a low battery charge or as they age over time, which can result in the device unexpectedly shutting down to protect its electronic components.
Last year we released a feature for iPhone 6, iPhone 6s and iPhone SE to smooth out the instantaneous peaks only when needed to prevent the device from unexpectedly shutting down during these conditions. We’ve now extended that feature to iPhone 7 with iOS 11.2, and plan to add support for other products in the future."
In any case, it's frustrating when your iPhone is slow! The best fix? Replacing your battery.
Getting a new battery (which costs $79 out of warranty through Apple or less with a third-party, non-authorized service provider) will likely improve your iPhone's performance significantly. It's a lot cheaper than getting a brand new phone!
Look what a battery replacement did for this guy!
If you're wondering if your older iPhone is experiencing battery decay, you can use Battery Life or Geekbench 4 ($1) to run battery benchmark tests.
Apple Support can also run a remote test that will check your iPhone’s overall battery health.