Here's what I think (hope) will be my final update to my adventure of finding a decent mp3 player...
After having the LG V20 for about a week, I took an out of town trip for about a week. The device was on, and I listened to music via GMMP for the entire three hour flight. The battery life dropped by a little less than ten percentage points. Same on the flight back. When carrying on my business, it was on for probably four or five hours every day and only needed to be charged once.
Bottom line is that I'm really happy with this solution and I should've listened sooner to the folks who suggested it.
Thank you all.