It is possible that the battery was damaged by external causes such as a failed power cable. First off, I would replace the battery (whether it is covered under warranty would be up to ifixit). Second, I would replace my charger and cable to rule out those as an issue. You may be getting improper voltages that are causing premature degradation of the battery and in your case, swelling.
Make sure you are using a quality solder and flux. Also, ensure your air is high enough to move the heat properly. You should be using leaded solder to do this repair. Make sure to use solder braid to remove all original solder. When in doubt, use more flux. Just make sure to clean it off after.
This sounds like you just have a bridged connector. Apply flux and heat and it should pull the solder to where it needs to be. I would always be safe and replace the port again though. there could be solder in places it should not be where you cant see it.
Hello, you have a faulty sleep/wake sensor. This is a solder component on the digitizer itself. It can be replaced, but it is much easier to just replace the digitizer again with a high quality part. I have had this issue with cheaper vendors before.
There is a backlight driver chip on the board that is likely water damaged. When this becomes damaged on the older models, you could test by shining a light through the apple logo and you would see display. Since the newer models use metal for the logo on the lid, this is not a viable option. My first place to look would be around this chip for corrosion. If there is none, I would replace the display.
First and foremost, you need to replace the battery. Be careful with this as the batteries on the 2015 pros are adhered in and are a pain to remove. I recommend liberal amounts of 99%ipa. Second. Make sure you have the proper voltage adapter. If you have an undervolted adapter it will not provide enough power. I also recommend using an OEM adapter.
Hello, many people forget to replace their thermal compound after cleaning the device. I would clean off the original compound and replace it with a better one any ways. I use thermal grizzly kryonaut personally but there are many compounds that are recommended for this applications. Also, make sure that all the thermal pads that sit on top of the memory chips are in tact.