If you think your older iPhone seems to run slower, you’re not crazy. Apple on Wednesday said a software feature released last year makes your phone operate more slowly to offset problems with its aging lithium ion battery.

As batteries get older, they don’t hold their charges as well as newer batteries, and can have worse problems when the charge is low or the temperature is cold.

The aging battery means your phone could have trouble operating or might unexpectedly shut down, like happened to the iPhone 6 and 6S last year. The processors in those devices wanted to hit faster speeds, but their batteries couldn’t handle the demand, prompting some phones to simply switch themselves off.

To address that, Apple’s iOS software, starting with last year’s iOS 10.2.1, included better power management capabilities, the company says. The operating system slows down your device to prevent it from shutting down, Apple says, but only in cases of cold temperature, a low battery charge or very old batteries.

Last year’s software applied to the iPhone 6 and 6 Plus, 6S and 6S Plus and SE. This year’s iOS 11.2 extended the feature to the iPhone 7 and 7 Plus. It will be applied to other Apple devices in the future.

iPhone users have long complained their devices seem to slow down when new models are released. Some have said they believe it to be effort by Apple (and other tech companies) to purposely hamper the performance in order to get users to buy new models. Apple has long denied this assertion.

For some people, the solution to a slower, older iPhone may be updating its battery instead of purchasing a brand new device. Apple charges $79 to replace the battery of an iPhone that’s no longer covered by a warranty.