Apple on Thursday released a letter apologizing to customers about the fact that it slows down old iPhones due to degraded batteries, calling the issue a “misunderstanding.” The company said beginning in January it will offer battery replacements for the iPhone 6 and newer for just $29.

Apple’s new pricing comes just days after evidence suggested the company was slowing down the performance of older iPhones, to which Apple ultimately admitted was true.

“We know that some of you feel Apple has let you down,” Apple said in the letter. “We apologize.”

According to Apple, the company has never intentionally shortened the lifespan of any Apple product, nor does it slow iPhones down in an effort to encourage people to upgrade their device.

“Our goal has always been to create products that our customers love, and making iPhones last as long as possible is an important part of that.”

The letter also makes a more concerted effort to educate iPhone owners as to why it slowed iPhones down in the first place, narrowing the problem down to aging batteries. As Apple said before, the company decided to slow the performance of older iPhones in an effort to avoid unexpected shutdowns, which could happen as a battery degrades.

“It should go without saying that we think sudden, unexpected shutdowns are unacceptable,” Apple said. “We don’t want any of our users to lose a call, miss taking a picture or have any other part of their iPhone experience interrupted if we can avoid it.”

Apple provides a more in-depth explanation as to why it decided to throttle performance in a support article. The company reveals that under extreme forms of power management, users will notice longer app launch times, lower frame rates, and more. Call quality, GPS performance, and Apple Pay aren’t impacted, Apple said.

When new pricing for Apple’s battery replacement program goes into effect, customers will have until December 2018 to take advantage, which means even iPhone X owners will be able to replace their battery after its one-year anniversary.

Additionally, Apple said it will issue an iOS update early next year “with new features that give users more visibility into the healthy of their iPhone’s battery.”