I would argue the whole point of Fairphone is to push the idea of Fairtrade. Repairabilty is attractive to some.
The SD card was probably down to your choice of formatting and nothing to do with the phone.
Likewise the battery usage, mine can last for days, depending how much time I’m on WhatsApp etc.
A test to see how the battery is being used is put it in aeroplane mode over night and see if there are any backgrounds apps running, be sure to close all apps. Hopefully you will find it only use 2 to 3 %. If that’s the case it will be your use rather than the battery that’s faulty.
As regards the second battery, if you keep swapping them the inbuilt algorithms will loose track of how much to charge each battery. The phone doesn’t record a battery ID and then when you swap batteries select the relevant algorithm.
You can try a kickstart on each battery to reset the monitoring.
The FP4 had a 25% larger capacity battery but a larger screen so it should not be much if any of an improvement.
Using WiFi ~ sit closer to the router so the transmitter uses less power. How good it the network signal. Do you have Wifi automatic setting and auto select which id better of WiFi or network.
Still unless you have lots of apps running then it’s likely usage is down to screen time, which may well only be 6 hours of continuos use.
You can read the battery usage to see what apps are actually draining it.
Hope you find something to help reduce the usage.
The account disabled is a concern and as each battery is guaranteed for two years.
Finally, can you find a fairphoneangel near you to confirm your discoveries and help analyse.
Here’s related topic about battery