Last year, Apple faced a scandal when it admitted it deliberately slowed down the performance of some iPhone device models to avoid battery problems. He later apologised and applied features that allow users to disable control. It also announced a battery replacement program, which allows users to afford a cheap replacement for the iPhone.
This program ends on 1 January 2019.
Basically, there are two ways to empty the battery before the end of the program: mail or personally at the Apple Store (or at Apple's authorised service centre). Here's a detailed description of everything you need to know. Among the possibilities, it seems personal, seems to be the best.
The first thing to do is schedule a meeting at a local Apple Store or Apple Authorized Service Center. You may want to make sure that the seller you are visiting has batteries in advance. If this is not the case, you can always contact Apple to send you the battery that will be delivered to the Apple store you are using. After you have arranged a meeting and make sure the battery is available, you should have trouble getting in and out of the store with the new battery on the same day.
The problem with the email version is that you will leave it without a phone for ten days. However, for this option, the first thing to do is contact Apple and send a box to send your phone. After this has been fixed, Apple told you that you could renew the phone for three to five business days. But does not include the time needed to return from your home to the repair centre.
So, there's the information you need to get a new battery, but you've got time to get it at a reduced rate, so hurry up.