Apple has slashed its iPhone battery replacement service fee to $29 from $79 after admitting to slowing down older models with worn-out batteries, but those looking to take advantage of the offer should know that the discounted pricing is limited to one repair per device.

According to new fine print on Apple’s iPhone Service Pricing webpage, which was discovered yesterday by MacRumros, the advertised $29 battery service fee “may be limited to one repair per iPhone” when an eligible device passes diagnostic test.

As the publication notes, this means that after you’ve had your iPhone’s battery replaced once this year at $29, the phone must explicitly fail the diagnostic test to qualify for any additional battery replacements for $29. “If the test passes, a customer can still choose to have the battery replaced, but Apple’s standard $79 fee applies,” reads the article.

As a quick refresher, iPhone batteries are designed to retain up to 80 percent of their original capacity at 500 complete charge cycles.

Devices that are eligible for the discounted battery service pricing include iPhone SE, iPhone 6s, iPhone 6s Plus, iPhone 7 and iPhone 7 Plus models.

Apple previously said that the $29 fee is valid through December 31, 2018.

As we previously reported, all Apple customers that request a battery replacement will get one, regardless of of the results of the battery diagnosis run on the device.

Nearly 30 class action lawsuits have been filed so far over the iPhone throttling debacle.

iPhone 7 teardown image courtesy of iFixit