The technology giants apologised to customers for slowing down older iPhones as the batteries aged, and has now clarified the rules and discount for those who swapped before the latest offer.
According to MacRumors, Apple has confirmed the replacements are valid regardless of the result of a diagnostic test, where previously it was required that a battery retained less than 80 per cent of its original capacity.
The offer - costing just $29 rather than the previous price of $79 - comes a month earlier than promised.
Meanwhile, an internal memo reportedly cited that customers who paid the full price prior to the latest development will be eligible for a refund of the price difference.
While battery condition won't be considered by Apple when it comes to a replacement, there will be some conditions to consider.
The company may not replace the battery if there is other damage to the phone, or if third-party components are found in the device.
A diagnostic can be run by Apple remotely, without the need to visit one of the brand's stores.
The process can be started by contacting Apple Support on the phone, or via email, online chat or Twitter.
Meanwhile, it's still also an option to schedule a Genius Bar appointment in-store via the Apple Support app.