Apple has confirmed that it ensures iPhones with older batteries slow down so that they do not start shutting down unexpectedly, The Verge reported, after Reddit users noticed a drop in the performance of their phones.

Geekbench developer John Poole wrote in a blog post that he had mapped out the performance of the iPhone 6S and iPhone 7 over time, and concluded that that Apple’s iOS 10.2.1 and 11.2.0 updates introduced this feature that slows down the devices.

While some users said it was a strategy adopted by Apple to force customers to upgrade their phones, the company denied it.

“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,” Apple said in a statement. “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.”

The tech giant said that this feature had been extended to iPhone 7 with iOS 11.2, and that it plans to add it to its devices in the future.