Shortened battery life, white spot on screen

The decreased battery life may be caused by a poor quality battery although in this case you purchased it from iFixit and they typically have good quality batteries. It is still possible that you have a dud and the easiest way to test it to try another one. That said, the excess heat points to something drawing excessive current, therefore decreasing battery life. You would have to do some tests to see what component is causing this. Start by disconnecting everything except the dock from the logic board when it is fully charged. Then let it discharge naturally and note the time it takes. Use a tool like 3uTools (www.3u.com) to periodically check the battery condition. Then add components like rear camera, screen and front camera one at time and replicate the test. If nothing changes, then you have an issue on the logic board, which will require a micro-soldering repair and is not DIY.

As for the white spot on the screen, that is caused by the water. This could be related to your battery issue (i.e. a bad backlight). If the above test does not indicate that the screen is the problem, then the only way to eliminate the white spot is to replace the screen.