When using headphones or any auxiliary plug in my LG G5, I get a static hissing noise.

My LG G5's battery life doesn't last the full day it is supposed to.

Hey Derek, The static noise is most likely caused by a faulty auxiliary cord, so you can replace that quickly and for cheap. Less likely, but possible, is a faulty auxiliary cord plug in. The plug in is modular to the phone, so removing it takes only about 20 minutes with minimal tools needed. There is a guide on this LG G5 page for doing that replacement. Then you could order and replace the plug in.

Poor battery life could be a result of a few causes. A few apps may be draining excessive power from your battery. You can check this by going to settings > Battery & power saving > Battery usage. This will show what apps are using the most power. From there, you can delete and change the settings for apps consuming too much power. Your G5 may have lots of cached data which can lower battery life. For this, got to Settings > General > Storage. Wait till it shows Cached Data, click it, and press yes to clear the data. At most, your battery may be faulty, in which case, take out the battery and replace it.