There's a very good business reason as to why Apple priced iPhone battery replacements at $79, and it isn't profit. By making a battery replacement relatively expensive, more existing iPhone owners with failing batteries are likely to decide to upgrade to a newer model instead, which is even more profitable for Apple. However, that situation is expected to change this year.
As Reuters reports, analysts at Barclays are expecting iPhone sales to drop during 2018 thanks to Apple's cheap battery replacement program which is already available. The iPhone 6 , 6 Plus, 6s, 6s Plus, 7, 7 Plus, and iPhone SE all qualify for the $29 battery replacement. Those models currently make up 77 percent of the iPhone market, meaning even a small percentage of owners opting for a new battery instead of a new iPhone will result in a significant fall in iPhone sales.
Apple lowered its battery replacement pricing as a way of saying sorry after having to admit it slowed down older iPhones without informing owners. This was done to help maintain battery life, not increase sales, but to users the experience was one of a handset that was getting slower (and a nudge to think about upgrading). Apple is now facing multiple lawsuits in response to the intentional performance throttling.
I think the knock-on effect of cheap batteries will extend beyond the end of 2018 when Apple's offer ends. Everyone who opts to have a $29 battery replacement will see their existing iPhone speed up again, demonstrating that you really don't need the latest model to continue enjoying the iOS experience.
So next time the phone gets slow, there's a greater chance of another battery replacement being selected (even at a higher price) than buying a new iPhone 8, iPhone X, or whatever comes next. And don't forget, even if you don't have an iPhone that qualifies for a cheap Apple battery because it is too old, iFixit is matching Apple's pricing and includes older models.