One of the few things you can count on is that Apple will release a new iPhone every year, a new and improved model that you just bought. By the time the new arrives, they are already classifying the old as outdated and dysfunctional. So contrary to popular belief, they don’t put that iOS 10 update on your iPhone 5s to make it better. “Planned obsolescence” is the term many people use to describe Apple’s decision to push problematic updates to all previous models to cause problems with batteries, apps that won’t open, connectivity, and other issues. These updates will slow down your phone, and with enough updates to an older model, it will become obsolete.
There is no reason why you can’t get four or five years out of your iPhone before upgrading to another. They are well-built, quality phones made to last. However, these upgrades can reduce service life by as much as two to three years. Therefore, anyone with a functional phone below the iPhone 7 should ignore these guidelines; ideally it should still be on iOS 8 or 9 for the iPhone 5 and 6 series. The software that comes with your phone already works perfectly fine.
Also remember that once you update, you will not be able to reverse it. Apple will try to force you to update in many ways. One of those tactics is that sometimes your phone will ask for the passcode, but you will write in fine print that doing so will automatically update the phone sometime early in the morning. Below, an even smaller button to opt out of this automatic update is the only way around it. Another means, even more difficult to avoid, is that developers will update popular applications such as Facebook and Snapchat to be compatible with the newer iOS, creating a disparity between their operating system and that of the application. To continue using it, you will most likely need to update your system. Wait as long as you can and then stop using the app or update, but stay informed about your choice.
The bottom line is that if you upgrade an older model, you can essentially turn it into a paperweight. The battery and charging port can be repaired, as can other things, but repair shops can only do so much with an updated phone because many times, the phone will just cut off new batteries or chargers. Be mindful of what you are doing with your phone, and also consider the impact of buying a new phone each year.