iPhone 6s (model A1633) Bluetooth Not working

I have had bad luck with ifixit batteries in the past, but I seriously doubt that is the cause of your bluetooth issue.

If you are also having issues with WiFi it could be the actual IC, as the same chip controls both.

Check your antenna connections at the top left (weird looking bracket on the logic board above the pwr/vol flex), and bottom right (diversity antenna sitting on top of the loudspeaker)

If all of that fails, it also never hurts to try a DFU reset. If you’re still having issues at that point you might need some board work done.

Is WiFi grayed out or is it just not finding anything? I will say I cannot think of a time where the actual antenna itself went bad, its too simple to really fail. WiFi module or boosters on the other hand could absolutely fail.