Apple’s exchange program for iPhone batteries at a low price has come to an end last year. At ifixit there are still low prices for do-it-yourselfers.
So ifixit promises in a Blogpost that they will keep the prices for all batteries down to the iPhone 4s low, so these cost a maximum of 29.99 dollars up to the iPhone 7. The batteries for the iPhone 8 around 50 dollars.
However, Apple’s 29 dollars also included the working time. If you have ever opened a glued iPhone 7, you will have appreciated that – and the current 49 dollars are not too much to ask for.
The prices for older iPhones are more interesting. For example, it’s worth picking a new one for the iPhone 5s: the battery costs 24.99 dollars at ifixit; the device is no longer listed at all on Apple’s website, but should fall under the “qualified models” and also cost 49 dollars there. There it is fairer to time value to make the exchange.