Originally Posted By: Phoenix42
SWMBO and I are iPhone users, used iPhone users, I with a 5S and she with a 5. The 5S is still on the original battery, which will be 4yrs old in March, and while it does get me through a typical day, it does not get me through a travel or conference day of heavier usage. SWMBO's 5 has had the battery replaced, thanks to ifixit for parts, tools, and instructions.

Both phones meet our needs, though the 5 stopped getting updates in July, and SWMBO is limited be the 16gb. Offering $29 battery upgrades (ifixit charges $20 for the battery alone) will likely be enough to sway us into upgrading to 6S by the end of 2018. Holding off that long because we're not heavy users - an out of date flagship phone does us just fine, I'm cheap, plus we hoping to build a new house in 2018 (which will be far from cheap).

I might have had a point when I started this post, but I'm not sure what it was now...
All iPhones were flagship models at some point (iPhone 5C excepted). Anything older than a 5s is running 32 bit software which means it is not getting iOS updates. No more security patches from Apple. And app updates from independent publishers may also wither away.

Stay off public WiFi and do not click on untrusted web links.

The time to sell the old iPhone 5 was much earlier in 2017 before Apple announced that iOS 11 would not support 32 bit hardware. Residual resale value in the iPhone 5 model I imagine has shrunk since.