Gee, that response up there was uncalled for. We're looking for solutions here and I think if you can't offer anything but an insult to someone else who had a suggestion, then your message was tons more worthless than what you thought the one you were replying to was.
I don't know - there might be something because I think you are right - the headphone jack is connected to the power - but I am not so sure that is the problem. It happened to me again today - charged it to green last night. Unplugged it all except for the headphones. This late morning, the battery meter was less than half. I did have my headphones connected this time. I recharged it again this morning, and after unplugging all, I didn't even have the headphones connected. It's about 12 hours later without use and the battery is still full. Hmmmmmm...
Either way, if it's a workaround, that would be certainly cool - but still a nuisance but at least it would make my battery life more predictable. It sucks to charge it the night before only to have little or no battery on your way to work the following day.
The way it's affecting people with 80g and 30g would definitely point to a firmware thing. I just hope/wish someone from Microsoft is monitoring these threads....