Intermittent "No Cell Coverage" issues after repair
I replaced both the battery and lightning/headphone port connector on my iPhone 6 and now have problems with the batter discharging quickly. Checking battery usage in "Settings", I've found "No Cell Coverage" is the culprit. Searching previous posts indicates it's possible the new lightning/headphone port is bad, or of course it's possible I made a mistake in reassembly. What all should I check regarding reassembly errors? Obviously there's the antenna cable connection, but I assume there could be other issues (e.g. how the lightning/headphone part connects to external antenna.)
I contacted iFixit support directly, but thus far all I've got back is a generic "Everything you need to know about replacing your iPhone battery" email. Just getting back into the phone is going to be a challenge, as after just one use of removing/reinstalling screws the pentalobe bit from the iFixit tools stripped. That's better than the screw heads being stripped, of course. I don't believe I used excessive force. I guess this is why they include the phillips head replacement screws that I unfortunately didn't use.