By Heather Kelly, CNN

Apple is working overtime to make amends with angry iPhone owners after revealing it slows down performance on older models.

People with an iPhone 6 or later can get a $29 replacement battery immediately — a month earlier than Apple originally planned to start offering discounted replacements. The company confirmed the early availability on Saturday.

"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," said an Apple spokesperson in a statement.

Last week, it was discovered that Apple was slowing down older iPhones on purpose. The company confirmed it was slowing performance at certain peak moments to prevent sudden battery shut downs. It said the power management feature, which was quietly rolled out in an iOS update last year, was only necessary for phones with aging lithium ion batteries. Swapping in a fresh battery should restore a phone back up to its normal speeds.

Customers were upset that the company did not tell them about the feature, and many thought it was an attempt to get people to upgrade to newer iPhone models. Some people are already suing Apple and seeking class action status.

In a letter to customers posted Thursday, Apple apologized for poor communication about the slowdown and denied it was an attempt to force upgrades. To make amends, Apple said it would offer the cheaper replacement batteries and working on a new iOS feature that will give users more information on their battery's status.

The batteries cost $29 instead of $79 and are available worldwide by going to an Apple Store or Apple certified retailer, or mailing a phone into Apple support. Apple originally said the batteries would be available at the $50 discount starting at the end of January. The lower prices are only available until the end of 2018.

The power management update was first rolled out a year ago to the iPhone 6, iPhone 6 Plus, iPhone 6S, iPhone 6S Plus and iPhone SE. Apple later added it for the iPhone 7 and iPhone 7 Plus.