I have an up to date 4s, but that means iOS 9.3.5. It works great, only problem is web browsing. Most sites load too much junk and can crash the phone. Brave is the only browser I can use, and it works pretty good for most sites.
I've never seen a phone where it isn't obviously somewhat impaired after 2 years, so what is it like on something that's 3 to 6 years old? Or do you get it replaced often?
I use a Third Rail case, so I can recharge easily. I don't use 3G, and all my apps work offline.
https://www.amazon.com/Third-Rail-Protective-Compatible-Rech...
One of the reasons I still like my phone is because of that case. I wish there was something similar for another phone. The external batteries also have microUSB in and out, so I can charge friends' phones too.
But replacing, not getting it replaced. At least on my 5 it is a few screws worth of work to swap.