WP8/L920 Battery Life Inconsistency

The battery life on my L920 (both before and after Portico update) has had extremely bipolar battery life.

Under nearly identical circumstances, I have two different stories to tell:

The story I don't like telling: Take the phone off the charger at 7am, whenever I use it throughout the day it is warm, and by the time I get home at 6pm that night, I am lucky to have 20% battery left.

The story I like telling: Take the phone off the charger at 7am, get home from work at 6pm with 90% battery left.

I am convinced this is a firmware issue and not hardware. The problem seems to be that the phone wants to go into a rapid discharge randomly. Sometime I think the battery is going to blow because of how insanely hot the device gets. It is at this time that I will see this rapid discharge. My week is repetitive enough that I over the past month I have been able to test this many times in the exact same scenario, and sometime the device may get hot when doing things, but battery life doesn't rapidly drop off, and I don't think the handset is going to blow. In the same situation the next day, the battery life drops insanely fast and I have to set the device down out of fear of explosion.

I have read reports around the internet, but the only solution I've heard is to swap the device. Anyone have a better idea? This would actually be the second device I have swapped, since the first one had red dots in dark parts of the images I captured.