Given, the Fairphone 2 is my backup device and not my daily driver, so my mileage will vary for sure. But I’m really using it from time to time, at least with every OS update, checking whether everything I want to work in case of need is still working, which involves considerable display on time with the update itself and a halfway demanding App like OsmAnd as well as a certain amount of browsing with Fennec, among other things. Sometimes I’m taking it with me because I expect getting called back on my secondary SIM card in it (in which cases I’ll use it like my daily driver for the time to see how it behaves … a backup which doesn’t work would be no backup).
Long story short, no overheating for me.
Battery life certainly isn’t great, but then it never was with this phone, and the decline of the charge still mirrors my use when I’m using it, nothing out of the ordinary to be seen on my side.
I tend to have a powerbank ready.
What you describe doesn’t sound normal to me, even with reasonably lowered expectations because of the age of the phone and/or the battery, unless there’s a real problem.
I have Discord running non-stop.
Signal doesn’t support multiple phones, so I’m not using it on my Fairphone 2.
Have you considered a factory reset or installing the OS from scratch (since a factory reset doesn’t touch the installed OS, just deletes user data as well as Apps installed by the user and their data)?
Perhaps keep this in mind if you intend to continue to use the phone (a not advisable life without Android security updates seems imminent). Software installations do age, too.
And SIM cards may deteriorate over time, which can cause very weird effects you would never quickly attribute to them. It might be worth a shot to check the behaviour of your phone with a different SIM card.
(Although as you say the phone of your wife showed exactly the same symptoms, it seems very much unlikely the SIM card would be at fault in both.)
The phone is definitely not secure anymore as Lineage OS also dropped support so very soon it’s going to become my back up anyway. Never heard of such effects caused by sim cards, interesting, I’ll keep that in mind. What are you using as your main phone currently?
I picked up my FP 5 for £505 brand new on eBay.