I also have this problem after I changed the Lightning assembly as described on iFixit. The phone now charges great, but the Settings > Battery shows that "No Cell Coverage" is hogging 30-40% of the battery. The phone will run through its entire charge from 100% to auto power off in about 8 hours, just sitting on a table not being used. Often "No Service" appears in the top left of the display, or "Verizon" either with either 0, 1, 2 dots or no dot display at all in the meter. It also occasionally displays "Extended". My wife has the same model phone, and none of this happens to her and her battery lasts 24 to 36 hours on a charge. The phones are the same age to the day. I've tried "Reset Network Settings", hard boot by holding the Power and Home buttons, removing and reinserting the SIM card with the phone both powered down and hot. All done several times, but the battery still drains like crazy. I suspect there is something wrong with the antenna connection somewhere. When I replaced the Lightning...

You'll need a small Phillips screwdriver. A size 0x40 works nicely. (Picture 1) Also get a penknife or Xacto knife to peel the gliders off, and some superglue of some type. To view the pictures larger, just single-click on them. They will zoom for a better view. (Picture 2) Remove the battery cover and the batteries. Remove the screws next to the + and - symbols. The other screws will be removed later. (Picture 3) Lift the edge of the foot gliders with a knife. Peel the sliders off. When you remove them, the adhesive will be useless. Rub it off with your finger and discard. Set the gliders aside. (Picture 4) Remove the screws that were hidden by the gliders. (Picture 5) Lift the upper shell away from the base. (Picture 6) Remove the two remaining screws that hold the blue top to the rest of the shell. (Picture 7) These screws are smaller than the four screws removed in prior steps. Keep them separate from the other four. (Picture 8) Push the 2 blue tabs toward the centerline of the mouse, using your...